Resource units for unassociated stations and grouped multi-user transmissions in 802.11ax networks

ABSTRACT

The invention relates to improve use of resource units in MU transmissions of an 802.11 ax network. An un-associated station may receive data frames over a downlink resource unit, RU, assigned to an AID, e.g. 2045, reserved for stations not associated with the AP, The AP may use a downlink RU sharing an allocation scheme feature of an uplink RU previously used by the un-associated station. The AP may also aggregated data frames addressed to several stations within the same downlink RU, for instance to acknowledge frames previously received from the stations. The aggregated data frames may signal which respective response RUs the addressee stations should use for a next multi-user uplink transmission to respond to the AP. These approaches particularly applies to the exchange of management frames for instance to speed up the association procedure of un-associated stations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat. Application No.17/816,971, filed on Aug. 2, 2022, which is a continuation of U.S. Pat.Application No. 16/606,676, filed on Oct. 18, 2019 and issued as U.S.Pat. No. 11,438,889 on Sep. 6, 2022, which is the National Phaseapplication of PCT Application No. PCT/EP2018/060250, filed on Apr. 20,2018 and titled “RESOURCE UNITS FOR UNASSOCIATED STATIONS AND GROUPEDMULTI-USER TRANSMISSIONS IN 802.11AX NETWORKS”. This application claimsthe benefit under 35 U.S.C. § 119(a)-(d) of United Kingdom PatentApplication No. 1706409.8, filed on Apr. 21, 2017, United Kingdom PatentApplication No. 1706408.0, filed on Apr. 21, 2017, United Kingdom PatentApplication No. 1716873.3, filed on Oct. 13, 2017, United Kingdom PatentApplication No. 1718496.1, filed on Nov. 8, 2017, United Kingdom PatentApplication No. 1802907.4, filed on Feb. 22, 2018, and United KingdomPatent Application No. 1806210.9, filed on Apr. 16, 2018. The abovecited patent applications are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationnetworks comprising an access point (AP) and stations and morespecifically to the transmission of data frames and/or acknowledgementthereof within a transmission opportunity made of sub-channels orResource Units, and corresponding devices.

The invention finds application in wireless communication networks, inparticular to the access of an 802.11ax composite channel and of OFDMAResource Units forming for instance an 802.11ax composite channel forDownlink communication from the access point to the stations. Oneapplication of the method regards wireless data communication over awireless communication network using Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA), the network being accessible by aplurality of station devices.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC family of standards (a/b/g/n/ac/etc.) defines a waywireless local area networks (WLANs) work at the physical and mediumaccess control (MAC) level. Typically, the 802.11 MAC (Medium AccessControl) operating mode implements the well-known DistributedCoordination Function (DCF) which relies on a contention-based mechanismbased on the so-called “Carrier Sense Multiple Access with CollisionAvoidance” (CSMA/CA) technique.

More recently, Institute of Electrical and Electronics Engineers (IEEE)officially approved the 802.11ax task group, as the successor of802.11ac. The primary goal of the 802.11ax task group consists inseeking for an improvement in data speed to wireless communicatingdevices (or stations) used in dense deployment scenarios.

In this context, multi-user (MU) transmission has been considered toallow multiple simultaneous transmissions to/from different stations(i.e. users) registered with the AP, in both downlink (DL) and uplink(UL) directions from/to the AP, during a transmission opportunitygranted to the AP over a 20 MHz (or more) communication channel.

In the uplink, multi-user transmissions are used to mitigate thecollision probability. This is because multiple non-AP stations areallowed to transmit simultaneously.

To actually perform such multi-user transmission, it has been proposedto split a granted communication channel (or transmission opportunitygranted to the AP) into sub-channels, also referred to as resource units(RUs), that are usually shared in the frequency domain between multipleusers (non-AP stations/nodes), based for instance on OrthogonalFrequency Division Multiple Access (OFDMA) technique.

Both multi-user Downlink OFDMA and Uplink OFDMA mechanisms offeroverhead reduction as key benefit.

To perform multi-user (MU) Downlink OFDMA transmission, the AP sends anMU packet over the whole granted communication channel, meaning that,from an RU point-of-view, the same preamble is transmitted. Next,RU-dependent payload is sent by the AP, meaning the payload varies fromone RU to the other, within the whole granted communication channel. Theassignment of the RUs to the stations is signalled at the beginning ofthe MU Downlink frame, by providing an association identifier (AID) of astation for each RU defined in the transmission opportunity.

Such an AID is individually obtained by each station when registering orassociating with the AP during an association procedure, that is to saywhen the station joins the group of stations managed by the AP. Duringthe association procedure, the not-yet-associated station or“unassociated station” and the AP exchange a series of single user (SU)802.11 management frames in order to enter into an authenticated andassociated state for the station. A result of the association procedureis that an AID is assigned to the station, enabling it to use MUcommunications (resource units).

An AID is usually formed by the 11 least significant bits of a 12-bitidentifier.

One station is thus registered or associated with the AP and has an AID,or is not yet registered or unassociated with the AP and has no AIDuntil registration is completed.

A group of stations together with the access point is known as a BasicService Set (BSS). To be noted that the range of available AlDs has tobe shared between the several groups of stations (i.e. several BSSs)that could be handled by the same physical access point whichinstantiates virtual access points for respective BSSs.

The stations receiving the MU Downlink frames within respective assignedRUs may have to acknowledge receipt thereof during a multi-user (MU)Uplink OFDMA transmission that follows the MU Downlink OFDMAtransmission within the same transmission opportunity.

To perform multi-user (MU) Uplink OFDMA transmission, the AP sends acontrol frame, known as Trigger Frame (TF), to the stations prior theycan access one RU assigned to them. The assignment of the RUs to thestations is signalled in a similar way as above (for Downlinktransmission using AIDs), but in the payload of the TF packet.

As a station is usually provided with a single transceiver, assignmentof multiple RUs to one and the same station shall not be allowed in802.11ax, for both multi-user Downlink and Uplink transmissions. Ofcourse a station with multiple transceivers could be assigned multipleRUs.

Thus, at most one RU is assigned to a station in the 802.11ax context,with all the stations being offered the same RU length. This has severalimplications.

In the specific case of MU Downlink acknowledgment through an MU Uplinktransmission, the AP does not use a separate trigger frame. Rather, theAP directly indicates, in the data frames sent over each RU of the MUDownlink transmission, which RU the receiving station must use in thefollowing MU Uplink OFDMA transmission to acknowledge the data frames.This specific indication is carried by a so-called UMRS field (standingfor UL MU Response Scheduling) provided in at least one data frame ofeach MU Downlink RU.

With respect to the multi-user Uplink OFDMA transmission, the AP doesnot know how much data each station has to transmit. 802.11ax thusrequires that the AP provides, in the Trigger Frame to the stations, anindication on the size of the requested (and granted) transmissionopportunity, i.e. how long each station can transmit data in itsallocated RU.

With respect to the multi-user Downlink OFDMA transmission, the AP mayhave different amounts of data to transmit to the stations. The AP maythus have to add padding bits to the shortest packets, until thetransmission opportunity ends.

Padding should be avoided as it is a waste of bandwidth.

Also, the association procedure introduced above appears to be bandwidthconsuming. This is mainly because the SU management frame aretransmitted at low bit rate (usually the lowest supported data rate)over the 20 MHz channel, in order for legacy stations (i.e. notimplementing 802.11ax) to be able to understand the common 802.11preamble. This is also because each SU management frame requires aspecific access to the medium by the station, and thus requires for thestation to wait until being granted a new medium access. As the numberof BSSs increases in the same area and/or as the number of stationswithin a BSS substantially increases, more channel bandwidth is lost dueto such SU signaling, and the cost to access the medium by the stationsincreases.

Recently, the 802.11ax task group has proposed a mechanism for the AP toreserve one or more RUs of a multi-user Uplink OFDMA transmission fornot-yet-associated or “unassociated” stations (which are 802.11 axcompliant). This is for these stations to speed up their registration tothe AP, by transmitting request management frames over such reserved RUs(in MU Uplink OFDMA mode). The proposed mechanism relies on the use of apredefined AID value equal to 2045 to indicate the random RUs thenot-yet-associated stations can access through contention.

Even with this new mechanism, the response management frames from the APare performed using low bit rate SU signaling. This is because, byfailing to have an own AID, these not-yet-associated stations cannot beassigned with RUs in a MU Downlink transmission. It remains that channelbandwidth is still wasted.

In addition, 802.11 does not provide mechanisms for multicast traffic,while the AP may receive multicast frames from an upper OSI layer, e.g.the link layer implementing Ethernet multicast. In that case, the AP hasto generate a plurality of data frames including payload of the receivedmulticast frame, to be each individually addressed to a respective oneof the addressee stations (of the multicast frame). Next, each dataframe is transmitted in a dedicated RU of the multi-user Downlink OFDMAtransmission, thereby resulting in duplicating several times the samepayload data over several RUs. Again, channel bandwidth is wasted.

The current operating mode of the 802.11 ax multi-user feature is thusnot fully satisfactory, for at least the above downsides regarding thepadding bits, the SU signaling for registration and the frameduplication for multicast traffic.

SUMMARY OF INVENTION

It is a broad objective of the present invention to efficiently improvethis situation, i.e. to overcome some or all of the foregoinglimitations. In particular, the present invention seeks to provide amore efficient usage of the MU Downlink transmission from the AP.

The Multi-User Downlink communication protocol may be enhanced to allowstations to efficiently identify their RUs in the MU Downlinktransmission from the AP where no AID can be used. This is for instancethe case for not-yet-associated or unassociated stations.

This approach proposes enhanced wireless communication methods in awireless network comprising an access point and stations.

In embodiments, any station registering or associating with the accesspoint being associated with or assigned a unique association identifierused by the access point to assign, to the station, a resource unit in atransmission opportunity granted to the access point, and the methodcomprises the following steps, at one of the stations:

-   determining a downlink resource unit assigned to an association    identifier reserved for stations not associated with the access    point (meaning the AID is at least not associated with a specific    station), from a plurality of downlink resource units comprised in a    multi-user downlink transmission from the access point within a    transmission opportunity granted to the access point; and-   receiving a (one or more) frame from the access point on the    determined downlink resource unit.

In other embodiments, the method comprises the following steps, at oneof the stations:

-   sending a frame to the access point using an uplink resource unit of    a plurality of uplink resource units provided in a multi-user uplink    transmission towards the access point within a transmission    opportunity granted to the access point, wherein the plurality of    uplink resource units are distributed according to an allocation    scheme;-   determining, based on at least one allocation scheme feature of the    uplink resource unit, a downlink resource unit from a plurality of    downlink resource units comprised in a multi-user downlink    transmission from the access point within a transmission opportunity    granted to the access point; and-   receiving a (one or more) frame from the access point on the    determined downlink resource unit.

From the AP perspective, an enhanced wireless communication method in awireless network comprising an access point and stations is alsoproposed.

In embodiments, any station registering or associating with the accesspoint being associated with or is assigned a unique associationidentifier used by the access point to assign, to the station, aresource unit in a transmission opportunity granted to the access point,and the method comprises the following steps, at the access point:

-   building a plurality of downlink resource units in a multi-user    downlink transmission from the access point within a transmission    opportunity granted to the access point, the plurality of downlink    resource units comprising a downlink resource unit assigned to an    association identifier reserved for stations not associated with the    access point (meaning the AID is at least not associated with a    specific station); and-   sending a frame to a station on the downlink resource unit assigned    to an association identifier reserved for stations not associated    with the access point.

In other embodiments, the method comprises the following steps, at theaccess point:

-   receiving a frame from a station on an uplink resource unit of a    plurality of uplink resource units comprised in a multi-user uplink    transmission towards the access point within a transmission    opportunity granted to the access point, wherein the plurality of    uplink resource units are distributed according to an allocation    scheme;-   building a plurality of downlink resource units in a multi-user    downlink transmission from the access point within a transmission    opportunity granted to the access point, the plurality of downlink    resource units comprising a downlink resource unit having at least    one matching allocation scheme feature with the uplink resource    unit; and-   sending a frame (usually a response to the frame received on the    uplink RU) to the station on the downlink resource unit.

802.11ax already proposes a prefixed number of RU allocation schemes fora 20 MHz channel, that each defines a specific distribution of RUs (e.g.in terms of RU size, frequency band, RU positions along the frequencydirection in 802.11ax) within the 20 MHz channel. The RU allocationscheme is for instance declared in the HE-SIG-B field of the MU Downlinkframe or in an equivalent field of a trigger frame.

Different RU allocation schemes may be used for each 20 MHz channelforming a composite channel of 40 MHz or 80 MHz or 160 MHz width.

By using a downlink RU that matches, according to some RU allocationscheme criteria/features, an uplink RU already used, AID is no longerneeded for the station to identify, in a Downlink transmission, whichdownlink RU to listen to. This is particularly advantageous forcommunication with stations which have not yet been associated with theAP (i.e. which have no AID).

In the other embodiments, by using AID not associated with stationsduring MU Downlink transmissions, the proposed method offers the AP withthe opportunity to address stations deprived of AID, such as stationsnot associated with the AP. The AID not associated with specificstations may then be reserved for stations not associated with the APfor particular embodiments. Again, such stations may easily identify, ina Downlink transmission, which downlink RU to listen to.

As extensively described below, these approaches may be implementedduring the association procedure for such not-yet-associated stations.As a result, medium occupancy and global latency for the associationprocedure are substantially reduced in an 802.11ax network.

MU Downlink transmission is thus significantly improved compared toknown 802.11ax current requirements.

Also, there is provided a wireless communication device forming stationin a wireless network comprising an access point and stations.

In embodiments, any station registering or associating with the accesspoint being associated with or is assigned a unique associationidentifier used by the access point to assign, to the station, aresource unit in a transmission opportunity granted to the access point,and the device forming station comprises at least one microprocessorconfigured for carrying out the steps of:

-   determining a downlink resource unit assigned to an association    identifier reserved for stations not associated with the access    point (meaning the AID is at least not associated with a specific    station), from a plurality of downlink resource units comprised in a    multi-user downlink transmission from the access point within a    transmission opportunity granted to the access point; and-   receiving a frame from the access point on the determined downlink    resource unit.

In other embodiments, the device forming station comprising at least onemicroprocessor configured for carrying out the steps of:

-   sending a frame to the access point using an uplink resource unit of    a plurality of uplink resource units provided in a multi-user uplink    transmission towards the access point within a transmission    opportunity granted to the access point, wherein the plurality of    uplink resource units are distributed according to an allocation    scheme;-   determining, based on at least one allocation scheme feature of the    uplink resource unit, a downlink resource unit from a plurality of    downlink resource units comprised in a multi-user downlink    transmission from the access point within a transmission opportunity    granted to the access point; and-   receiving a frame from the access point on the determined downlink    resource unit.

Also, there is provided a wireless communication device forming accesspoint in a wireless network comprising an access point and stations.

In embodiments, any station associating with the access point isassigned a unique association identifier used by the access point toassign, to the station, a resource unit in a transmission opportunitygranted to the access point, and the device forming access pointcomprises at least one microprocessor configured for carrying out thesteps of:

-   building a plurality of downlink resource units in a multi-user    downlink transmission from the access point within a transmission    opportunity granted to the access point, the downlink plurality of    resource units comprising a downlink resource unit assigned to an    association identifier reserved for stations not associated with the    access point (meaning the AID is at least not associated with a    specific station); and-   sending a frame to a station on the downlink resource unit assigned    to an association identifier reserved for stations not associated    with the access point.

In other embodiments, the device forming access point comprising atleast one microprocessor configured for carrying out the steps of:

-   receiving a frame from a station on an uplink resource unit of a    plurality of uplink resource units comprised in a multi-user uplink    transmission towards the access point within a transmission    opportunity granted to the access point, wherein the plurality of    uplink resource units are distributed according to an allocation    scheme;-   building a plurality of downlink resource units in a multi-user    downlink transmission from the access point within a transmission    opportunity granted to the access point, the plurality of downlink    resource units comprising a downlink resource unit having at least    one matching allocation scheme feature with the uplink resource    unit; and-   sending a frame (usually a response to the frame received on the    uplink RU) to the station on the downlink resource unit.

Optional features of these embodiments are defined in the appendedclaims with reference to methods. Of course, same features can betransposed into system features dedicated to any device according to theembodiments of the invention.

In embodiments for the station, a plurality of downlink resource unitsare determined at the determining step (it may be considered that thereis an RU-based aggregation of the data frames over the plurality ofdownlink RUs), and wherein the method may further comprises retrievingone or more data frames from one of the plurality of determined downlinkresource units.

In embodiments for the station, the method may further comprises, at thestation, sending a frame to the access point using an uplink resourceunit of a plurality of uplink resource units provided in a multi-useruplink transmission towards the access point within a transmissionopportunity granted to the access point, wherein the plurality of uplinkresource units are distributed according to an allocation scheme. Inthat case, determining the downlink resource unit assigned to anassociation identifier not associated with a specific station, and inparticular reserved for stations not associated with the access point,may also be based on at least one allocation scheme feature of theuplink resource unit.

Conversely for the AP, the method may further comprises, at the accesspoint, receiving a frame from a station on an uplink resource unit of aplurality of uplink resource units provided in a multi-user uplinktransmission towards the access point within a transmission opportunitygranted to the access point, wherein the resource units of the pluralityof uplink resource units are distributed according to an allocationscheme. In that case, the downlink resource unit assigned to anassociation identifier not associated with a specific station, and inparticular reserved for stations not associated with the access point,in the built plurality of downlink resource units may have at least onematching allocation scheme feature with the uplink resource unit.

In some embodiments, determining the downlink resource unit is based ona number of downlink resource units assigned to the associationidentifier reserved for stations not associated with the access point,in the multi-user downlink transmission.

In one implementation, if the number of downlink resource units is one,the single downlink resource unit assigned to the association identifierreserved for stations not associated with the access point is selectedas being the determined downlink resource unit for receiving the frame.

In one implementation, if the number of downlink resource units is morethan one, one downlink resource unit assigned to the associationidentifier reserved for stations not associated with the access point isselected as being the determined downlink resource unit for receivingthe frame, wherein the selecting is based on at least one allocationscheme feature of an uplink resource unit used by the station to send aframe to the access point. The uplink resource unit may be one among aplurality of uplink resource units provided in a multi-user uplinktransmission towards the access point within a transmission opportunitygranted to the access point, and wherein the plurality of uplinkresource units are distributed according to an allocation scheme.

In some embodiments, and preferably (but not only) when it is determinedthe multi-user downlink transmission comprises a single determineddownlink resource unit assigned to the association identifier reservedfor stations not associated with the access point, the station mayfurther comprise checking whether the frame received in the determineddownlink resource unit is addressed to the station, prior to decodingthe frame. It means the station further comprises checking whether thedetermined downlink resource unit contains a frame addressed to thestation, so to trigger the receiving, and subsequent decoding, of theframe in case of a positive checking. This approach is to discard aframe if it is not addressed to the station.

In embodiments related to the association procedure of stations with theAP, the station is not associated with the access point, and the framein the uplink resource unit is a request management frame in a processof associating the station with the access point, while the frame in thedownlink resource unit is a response management frame in response to therequest management frame. In this context, the embodiments substantiallyimprove the global latency for the association procedure.

In some embodiments, the allocation scheme feature includes a positionof the resource unit in the corresponding plurality of resource units,according to the allocation scheme. For instance, if the uplink resourceunit corresponds to RU at position #3 in the RU allocation scheme (asindicated in a trigger frame triggering the MU Uplink transmission), thedownlink resource unit for downlink transmission may be the one atposition #3 in the plurality of downlink RUs. This may be regardless ofwhether the two RUs share the same frequency range (or range of tones)or not.

This feature or criterion is easily identified by the AP and thestation, while requiring little information to temporarily store fromthe uplink RU in order to build the downlink RU.

In variants, the allocation scheme feature includes a frequency band ofthe resource unit in the corresponding plurality of resource unitsdistributed in the frequency domain according to the allocation scheme.This may be regardless of whether the two RUs share the same position intheir respective plurality of RUs. For instance the downlink RU hasexactly the same tones as the uplink RU, within the considered 20 MHzchannels. Also, it may be contemplated having the downlink RU startingat or ending with exactly the same tone as the uplink RU (even if theirRU sizes are different).

This feature or criterion is easily identified by the AP and thestation, while requiring little information to temporarily store fromthe uplink RU in order to build the downlink RU.

In other variants, the allocation scheme feature includes a size of theresource unit in the corresponding plurality of resource units,according to the allocation scheme. For instance, if the uplink RU is52-tones width, the downlink RU can be identified as being one (or theone) being also 52-tones width. It may be noted that one or more othercriteria may be used to identify the right downlink RU from amongstseveral candidates (for instance if several 52-tones width RUs aredefined in the plurality of downlink RUs). An exemplary other criterionis a predefined AID assigned to the downlink RU, as introduced below.

Of course, all or part of the position criterion, frequency bandcriterion and size criterion may be combined to determine or build thedownlink RU relatively to the uplink RU.

In some embodiments, any station registering or associating with theaccess point is associated with or assigned a unique associationidentifier used by the access point to assign, to the station, aresource unit in a transmission opportunity granted to the access point,and the uplink and/or downlink resource units are assigned to apredefined association identifier not associated with a specificstation, and in particular reserved for stations not associated with theaccess point. Although the predefined association identifier is notdedicated to a specific station, it makes it possible for the stations(e.g. not-yet-associated stations) to quickly identify an uplink RUaccording to these embodiments and to verify the allocation schemefeature on few RUs to find the appropriate downlink RU. This reducesprocessing at the station.

In specific embodiments, the uplink and downlink resource units areassigned to the same predefined association identifier not associatedwith a specific station, in particular reserved for stations notassociated with the access point. This is to simplify the processing atboth the AP and the stations.

According to a specific feature, the association identifier notassociated with a specific station is an 11-bit identifier equal to2045. In a particular case, this association identifier is reserved forstations not associated with the access point.

In some embodiments, the pluralities of uplink and downlink resourceunits belong to the same transmission opportunity granted to the accesspoint. This approach reduces latency in a frame exchange initiatedbetween the AP and the station (e.g. related to an associationprocedure).

In specific embodiments, the plurality of downlink resource units in themulti-user downlink transmission directly follows the plurality ofuplink resource units comprised in the multi-user uplink transmissionwithin the same transmission opportunity granted to the access point.This means without intermediary (downlink or uplink) resource unitsbetween them. This however does not exclude the presence ofacknowledgment. This approach optimizes the latency.

In variants, the plurality of uplink resource units comprised in themulti-user uplink transmission and the plurality of downlink resourceunits in the multi-user downlink transmission are separated by at leastone third plurality of resource units provided for a multi-user uplinkor downlink transmission within the same transmission opportunitygranted to the access point. It makes it possible for the AP to scheduleintermediary MU Downlink or Uplink transmissions within the same TXOP,to improve exchanges with the stations.

In other variants, the pluralities of uplink and downlink resource unitsbelong to different transmission opportunities granted to the accesspoint. This may give to the AP enough time to prepare the responses tothe not-yet-associated stations that have sent requests through aso-called “uplink RU” of an MU Uplink transmission.

In some embodiments, the resource units of each plurality aredistributed in the frequency domain according to the respectiveallocation scheme. This applies to the RUs defined in 802.11ax.

In some embodiments, the plurality of uplink resource units provided inthe multi-user uplink transmission is triggered in the transmissionopportunity by a trigger frame sent by the access point. Thisparticularly applies to 802.11ax networks.

The Multi-User Downlink communication protocol may also be enhanced tosupport a multiplicity of addressee stations for the same Downlink RU,including those stations which have not yet received an AID (i.e. notyet registered or associated with the AP).

This approach (referred below as the aggregation-based approach)proposes enhanced wireless communication methods in a wireless networkcomprising an access point and stations.

In embodiments, the method comprises the following steps, at one of thestations:

-   determining a resource unit dedicated to a plurality of stations,    from amongst a plurality of resource units forming a multi-user    downlink transmission opportunity granted to the access point for    downlink communication to the stations;-   receiving aggregated data frames over the determined resource unit;    and-   retrieving one or more data frames addressed to the station, from    amongst the received aggregated data frames.

From the AP perspective, enhanced wireless communication methods in awireless network comprising an access point and stations are alsoproposed.

In embodiments, the method comprises the following steps, at the accesspoint:

-   aggregating data frames addressed to two or more stations; and-   transmitting the aggregated data frames over a resource unit    dedicated to a plurality of stations, from amongst a plurality of    resource units forming a multi-user downlink transmission    opportunity granted to the access point for downlink communication    to the stations.

With these new RU-based transmission schemes, the inventors provide acommunication mechanism that supports a multiplicity of addresseestations for the same Downlink RU, including those stations which havenot yet received an AID (i.e. not yet registered or associated with theAP).

MU Downlink transmission is thus significantly improved compared toknown 802.11 ax current requirements. Indeed, by combining data framesto be addressed to several stations within the same dedicated RU,embodiments of the invention make it possible for the AP to efficientlytarget a large number of stations, thereby using more efficiently eachRU (and thus reducing padding bits), avoiding duplicating the samepayload over several RUs (in case of multicast) and/or efficiently (i.e.at a higher bit rate) providing response management frames to thenot-yet-associated stations.

Such a RU dedicated to multiple addressee stations may be named “group”RU (or “multicast” RU) in comparison to classical “individual” RUs eachof which being assigned to a single station.

In practice, such group RUs may be used to convey various types of dataframes, including broadcast frames (the same frames intended to allstations), multicast frames (the same frames intended to multiplestations) or even multiple unicast frames (multiple frames, eachintended to a single station).

Also, there is provided a wireless communication device forming stationin a wireless network comprising an access point and stations.

In embodiments, the device forming station comprising at least onemicroprocessor configured for carrying out the steps of:

-   determining a resource unit dedicated to a plurality of stations,    from amongst a plurality of resource units forming a multi-user    downlink transmission opportunity granted to the access point for    downlink communication to the stations;-   receiving aggregated data frames over the determined resource unit;    and-   retrieving one or more data frames addressed to the station, from    amongst the received aggregated data frames.

Also, there is provided a wireless communication device forming accesspoint in a wireless network comprising an access point and stations.

In embodiments, the device forming access point comprising at least onemicroprocessor configured for carrying out the steps of:

-   aggregating data frames addressed to two or more stations; and-   transmitting the aggregated data frames over a resource unit    dedicated to a plurality of stations, from amongst a plurality of    resource units forming a multi-user downlink transmission    opportunity granted to the access point for downlink communication    to the stations.

In this aggregation-based approach, an issue remains with respect to theframe acknowledgment for the group RUs.

Indeed, in the conventional 802.11ax acknowledgment mechanism, theacknowledgment of data frames received over an RU is made by the stationto which the RU has been assigned over an RU in the following MU UplinkOFDMA transmission as indicated in the UMRS field (received in theDownlink RU). However, this mechanism cannot operate for group RUs, asno specific station is designated as the RU assignee. Furthermore, evenif one station would be so designated, it should not be allowed toacknowledge the data frames addressed to other stations of the group RU.

Intuitively, other solutions are possible. However, they are notefficient.

For instance, the response frames (here acknowledgments) from theaddressee stations of the group RU may be triggered later on by the AP.This can be performed by individual SU exchanges between the AP and eachaddressee station. However, SU exchanges are not efficient in term ofbandwidth use: channel bandwidth is still wasted.

Alternatively, the AP may emit a following trigger frame to offer RUsfor the addressee stations to acknowledge previous MU Downlink OFDMAtransmission from the AP. However, by failing to have an own AID,not-yet-associated addressee stations cannot be offered scheduled RUs,and thus may rely on random RUs only which are subject to poorefficiency due to contention. Not-yet-associated addressee stations maythus not be in position to efficiently acknowledge data frames receivedwithin a group RU of a MU Downlink OFDMA transmission (here below aDownlink group RU or DL group RU). A consequence is that the AP willretransmit the not-acknowledged data frames: channel bandwidth is stillwasted.

To overcome such drawbacks, enhanced methods and devices are proposed bythe inventors with the aim of providing an efficient acknowledgmentmechanism, from which better usage of the OFDMA MU transmission by theAP can be obtained.

In this context, an enhanced wireless communication method of the aboveaggregation-based approach is proposed that further comprises, at theaccess point, the step of signalling, in two aggregated data framesaddressed to two respective stations, respective response resource unitinformation identifying a response resource unit to be used by theaddressee station in a multi-user uplink transmission opportunityfollowing the multi-user downlink transmission opportunity to provide aresponse to data frames to the access point.

Conversely, an enhanced aggregation-based method at the station furthercomprises the step of:

-   obtaining, from the retrieved data frames, response resource unit    information identifying one response resource unit in the multi-user    uplink transmission opportunity, and-   sending to the access point a response to the retrieved data frames    over the identified response resource unit.

For instance, the response resource unit information is signalled in theUplink Multi-user Response Scheduling (UMRS) control subfield of a dataframe as defined in the 802.11ax, version 2.0, standard (officiallyknown as Draft P802.11ax_D2.0, in particular section 9.2.4.6.4.2 “UMRSControl”).

Contrary to the 802.11ax requirements limiting a single value of UMRSper RU, these enhanced methods allow the various addressee stations (viagroup RU) to efficiently acknowledge receipt of data frames.

As the AP is able to schedule more RUs in the MU Uplink OFDMAtransmission than in the MU Downlink OFDMA transmission, it is possibleto provide an opportunity for all the addressee stations (even if DLgroup RUs are used) to acknowledge their received data frames.Retransmission of data frames by the AP is this avoided, thereby savingchannel bandwidth.

Also, this is the addressee station as specified in the RA field (MACaddress) of the frame MAC header that can use the response RU indicatedin the UMRS information of the same MAC header. As a consequence, eventhe addressee stations which are not yet associated with the AP canacknowledge data frames. The association procedure can thus besimplified for the stations (using random RU with AID=2045, receivingresponses from the AP during MU Downlink transmission, and acknowledgingthe response during subsequent MU Uplink transmission). In other words,the UMRS control field can be used inside each MPDU (MAC Protocol DataUnit) of the A-MPDU (Aggregate MPDU) indicating which UL RU must be usedby the unassociated station to acknowledge the MPDU(s).

Also, there is provided a wireless communication device forming stationin a wireless network comprising an access point and stations. Thedevice forming station comprises at least one microprocessor configuredfor carrying out the steps defined above for the enhancedaggregation-based method from station perspective.

Also, there is provided a wireless communication device forming accesspoint in a wireless network comprising an access point and stations. Thedevice forming access point comprises at least one microprocessorconfigured for carrying out the steps defined above for the enhancedaggregation-based method from AP perspective.

Optional features of these enhanced aggregation-based embodiments aredefined in the appended claims with reference to methods. Of course,same features can be transposed into system features dedicated to anydevice according to the embodiments of the invention.

In some embodiments, the enhanced aggregation-based method furthercomprises, at the access point, the step of receiving responses from theaddressee stations over resource units of the following multi-useruplink transmission opportunity, the response from an, preferably any,addressee station being received over the response resource unitidentified in the response resource unit information (UMRS) signalled ina data frame addressed to said addressee station within the transmittedaggregated data frames. Of course, similar response RU information canbe used for the stations addressed via individual RUs.

Preferably, the responses from the addressee stations includeacknowledgments of data frames of the transmitted aggregated dataframes.

In some embodiments, the multi-user uplink transmission opportunity andthe multi-user downlink transmission opportunity belongs to the sametransmission opportunity granted to the access point. A singlecontention to access the medium is thus required for the AP, therebysaving time and channel bandwidth.

In other embodiments, the enhanced aggregation-based method furthercomprises, at the access point, configuring the multi-user uplinktransmission opportunity in such a way it includes a number of responseresource units based on a number of stations addressed in the multi-userdownlink transmission opportunity. This makes it possible for the AP toprovide an opportunity for frame acknowledgment to desired addressedstations.

For instance, the enhanced aggregation-based method further comprises,at the access point, configuring the multi-user uplink transmissionopportunity in such a way it includes a number of response resourceunits that is at least (preferably the same as) a number of stationsthat have to provide a response to data frames addressed to them overany resource unit of the multi-user downlink transmission opportunity.This makes it possible for all the stations to provide an acknowledgmentto the AP.

For instance, stations that have to provide a response include thoseaddressee stations for which a respective response resource unitinformation is signalled in the aggregated data frames. In fact,stations that have to provide a response may be those compliant with theUMRS signalling and/or those to which UMRS information is provided inthe group or individual RUs of the MU Downlink transmission.

In some embodiments, aggregating data frames comprises aggregating dataframes to be addressed to a number of stations in such a way a totalnumber of stations addressed over the plurality of resource unitsforming the multi-user downlink transmission opportunity does not exceeda determined maximum number of stations. This configuration restrictsthe possibility for the AP to involve too many stations per group RU andthus in the whole MU Downlink transmission, in such a way not all ofthem will be able to acknowledge the data frames. As a consequence, dataframe acknowledgment is efficiently conducted, reducing the risks forthe AP to have to resend data frames correctly received (but not yetacknowledged).

In particular, the determined maximum number of stations may depend on(e.g. is equal to) a maximum number of elementary resource units thatcan be defined within the multi-user uplink transmission opportunity.The elementary resource units may be seen as the smallest RUs acceptablefor instance by the 802.11ax standard. In the latter, each 20 MHzchannel can be divided at most into nine elementary RU.

Optional features of the aggregation-based embodiments are also definedin the appended claims with reference to methods. Of course, samefeatures can be transposed into system features dedicated to any deviceaccording to the embodiments of the invention.

This aggregation-based approach may be combined with the first approachpreviously presented, in particular when using AID not associated withstations during MU Downlink transmissions to offer the AP with theopportunity to address stations deprived of AID, such as stations notassociated with the AP. In such combination where the station determinesa resource unit assigned to an association identifier not associatedwith a specific station, the method may further comprise, at thestation:

-   receiving aggregated data frames over the determined resource unit;    and-   retrieving one or more data frames addressed to the station, from    amongst the received aggregated data frames.

Correspondingly, at the access point, the method according to the firstapproach may further comprise:

-   aggregating data frames to be addressed to two or more stations; and-   transmitting the aggregated data frames over the resource unit    assigned to an association identifier not associated with a specific    station.

In embodiments, any station registering or associating with the accesspoint is associated with or assigned a unique association identifierused by the access point to assign, to the station, a resource unit in atransmission opportunity granted to the access point, and the resourceunit dedicated to a plurality of stations is assigned in the downlinktransmission opportunity to a predefined association identifier notassociated with a specific station. This may be seen as a “group AID”for a group of stations. All 802.11ax compliant stations may thus beaware of such predefined AID or AlDs, in order to scrutinize therelevant RU.

In some embodiments, the access point may set, in each data frame to beaggregated, a MAC address field to a MAC address of the addresseestation. This is to allow the addressee stations to efficiently retrievetheir own data frames. Indeed, from the station perspective, retrievingone or more data frames addressed to the station may thus includecomparing a MAC address of each aggregated data frame with a MAC addressof the station.

To avoid too much processing at the access point, the station may notacknowledge receipt of the retrieved data frames, to the access point.Thus all the data frames in the Downlink RU are not acknowledged.

In a variant, the station may send an acknowledgment of the retrieveddata frames only if the retrieved data frames include the last receivedaggregated data frame. It means that only the last data frame isexplicitly acknowledged by its corresponding receiving station, and theother data frames of the Downlink RU for the group of stations are thusimplicitly acknowledged as soon as the acknowledgment for the last oneis correctly received.

As introduced above, one application of this approach regards themanagement frames for the not-yet-associated (registered) stations toefficiently register with the access point. In this context, the stationmay, prior to determining a resource unit, send a management frame tothe access point within a procedure of associating (i.e. registering)the station with the access point. In such case, determining a resourceunit includes determining a resource unit assigned to stations not yetassociated with the access point, to retrieve a response from the accesspoint to the sent management frame. In other words, a resource unit inthe Downlink OFDMA transmission is reserved for the not-yet-associatedstations, from which RU they may obtain the responses to their requestmanagement frames.

This approach avoids using SU signalling even for the responsemanagement frames. Network bandwidth is thus saved.

From AP’s perspective, it may mean that the access point, prior to thestep of transmitting data frames, receives at least one management framefrom a station willing to associate (i.e. register) with the accesspoint, and the transmitted data frames include a response to thereceived management frame and are transmitted over a resource unitassigned to stations not yet associated with the access point.

To provide an enhanced association procedure, the management frame issent in a prior resource unit forming part of an uplink transmissionopportunity granted to the access point for uplink communication fromthe stations, the prior resource unit being assigned to stations not yetassociated with the access point. Thus, both request and responsemanagement frames can be sent in (high bit rate) MU OFDMA RUs, therebyreducing medium occupancy.

In some embodiments, the determined resource unit and the prior resourceunit are assigned in the downlink and uplink transmission opportunitiesrespectively, to the same prefixed association identifier not associatedwith a specific station, for instance AID=2045 or an associationidentifier associated with a basic service set (provided by the AP), forinstance equal to the basic service set identifier of the basic serviceset. This makes the management at the stations and the access pointeasier.

To further improve the association procedure, the station may send anacknowledgment of the retrieved data frames, in a next resource unitforming part of a next uplink transmission opportunity granted to theaccess point for uplink communication from the stations, the nextresource unit being assigned to stations not yet associated with theaccess point. This is an efficient way to provide, at low cost, anopportunity to each not-yet-associated station willing to register, toacknowledge receipt of response management frames (i.e. without using SUsignalling).

Another application of the present invention regards the management ofmulticast traffic or any residual traffic (i.e. small amounts of datathat would require padding bits given the RU size).

In the case of multicast traffic, the access point receives a multicastframe (e.g. from an upper OSI layer) to be addressed to a plurality ofaddressee stations. Next, responsive to the multicast frame reception,the access point generates a plurality of data frames including payloadof the multicast frame, to be each individually addressed to arespective one of the addressee stations. The aggregated data frames tobe transmitted over the resource unit dedicated to a plurality ofstations thus include the generated data frames including payload of themulticast frame.

For instance, the resource unit dedicated to a plurality of stations totransmit the aggregated data frames including the payload of themulticast frame may be assigned in the downlink transmission opportunityto a prefixed association identifier not associated with a specificstation equal to 2042.

In the case of residual traffic, the access point may determine smalldata frames to be transmitted to stations, given a size of the downlinktransmission opportunity (possibly the size of the RUs) and a sizethreshold. Thus, the determined small data frames are aggregated andtransmitted over the resource unit dedicated to a plurality of stations,referred to as collecting resource unit. For instance, the collectingresource unit is signalled in the downlink transmission opportunityusing a prefixed association identifier equal not associated with aspecific station to 0.

From the station perspective, both multicast and residual traffic can behandled in the same way. For instance, the station may first scanthrough resource units assigned to individual stations to verify whethera resource unit of the plurality is individually assigned to the stationor not, and in case of negative verification only, determining aresource unit dedicated to a plurality of stations from the not-yetscanned resource units of the plurality. In particular, determining aresource unit dedicated to a plurality of stations from the not-yetscanned resource units may comprise first scanning through resourceunits assigned to lists of stations to verify whether the stationbelongs to a list associated with one of the scanned resource units. Thelist may for instance correspond to a specific AID used as a group AID,each station being able to determine whether or not it belongs to suchgroup (for instance through bit masking or with reference to group AIDprovided by the AP upon registration).

Thus, in case of positive verification, the determined resource unit (toretrieve the data frames) is the one assigned to a list that includesthe station.

Also, in case of negative verification only, the determined resourceunit is a collecting resource unit used to convey data frames for anystation not assigned, individually or through a list, to anotherresource unit forming the downlink transmission opportunity.

These various approaches avoid duplicating the same data over severalRUs and/or reduce the amount of padding data to be added in the RUs.Consequently, medium use is made more efficient.

To ensure efficient processing by the stations, embodiments provide thatthe downlink transmission opportunity includes an ordered signalling ofassignments of resource units of the plurality to one or more stations,the ordered signalling first defining each assignment of a resource unitto an individual station, next defining each assignment of a resourceunit to a group of stations, then defining an assignment of thecollecting resource unit to any station not yet associated with aresource unit. Indeed, a station will thus first determine individualRUs, before (in case of negative verification) considering whether ornot a group RU has been used. Thus, only if no RU has been identifiedfor the station, the latter can scrutinize the collector RU (dedicatedto any station) to possibly retrieve some data addressed to it.

Thanks to this approach, a station may advantageously disregard anyfurther RU analysis in the same Downlink transmission opportunity, onceit has found one RU (individual or group) addressed to it.

Embodiments of the present invention may be implemented in all 802.11 axcompliant AP and non-AP stations. Alternatively, 802.11 ax compliant APand non-AP stations may optionally implement features of embodiments ofthe present invention.

In this context, and according to one implementation, there is provideda wireless communication method in a wireless network comprising anaccess point and stations, the method comprising the following steps, atthe access point:

-   receiving a capability information from one or more stations, the    capability information comprising the capability of a station to    allow a data frame addressed to the station to be aggregated with    one or more data frames addressed to one or more other stations;-   aggregating data frames based on the received capability    information; and-   transmitting the aggregated data frames to the one or more stations.

In a particular implementation, the transmitting is performed over aresource unit dedicated to a plurality of stations, from amongst aplurality of resource units forming a multi-user downlink transmissionopportunity granted to the access point for downlink communication tothe stations.

Preferably, the capability information is advertised in a managementframe during association procedure of the one or more stations to theaccess point.

For example, the capability information is signalled in a subfield ofthe HE MAC Capability Information field as defined in the 802.11 ax,version 2.1, standard.

In particular, if a station does not allow a data frame addressed to thestation to be aggregated with one or more data frames addressed to oneor more other stations, the aggregating comprising forming a data unitcomprising one or more data frame addressed only the station.

Conversely, there is provided a wireless communication method in awireless network comprising an access point and stations, the methodcomprising the following steps, at one of the stations:

-   transmitting a capability information to the access point, the    capability information comprising the capability of the station to    allow a data frame addressed to the station by the access point to    be aggregated with one or more data frames addressed to one or more    other stations;-   receiving aggregating data frames based from the access point; and-   extracting data frames from the received aggregated data frames,    wherein the extracting is based on the transmitted capability    information.

In a variant, the method further comprising, a step of receiving acapability information from the access point, the capability informationcomprising the capability of the access point to aggregate data framesaddressed to two or more stations.

Particularly, the extracting is further based on the capabilityinformation received from the access point.

In a particular implementation, the receiving is performed over aresource unit dedicated to a plurality of stations, from amongst aplurality of resource units forming a multi-user downlink transmissionopportunity granted to the access point for downlink communication tothe stations.

In particular, the capability information is advertised in a managementframe during association procedure of the station to the access point.For example, the capability information is signalled in a subfield ofthe HE MAC Capability Information field as defined in the 802.11ax,version 2.1, standard.

The one implementation concerns also a wireless communication deviceforming access point in a wireless network comprising an access pointand stations, and a wireless communication device forming station in thewireless network.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device, causes the device toperform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the methods and devices.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a typical wireless communication system in whichembodiments of the invention may be implemented;

FIGS. 2 a to 2 g present various formats of 802.11 frames according tothe 802.11 ax standard;

FIGS. 2 h to 2 j illustrate the UMRS Control field as defined in802.11ax;

FIG. 3 illustrates an exemplary sequence of management frames allowing anot-yet-associated station to discover and register with a given AccessPoint;

FIG. 4 illustrates 802.11ac channel allocation that support channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

FIG. 5 illustrates an example of 802.11ax uplink OFDMA transmissionscheme, wherein the AP issues a Trigger Frame for reserving atransmission opportunity of OFDMA sub-channels (resource units) on an 80MHz channel as known in the art;

FIG. 6 illustrates, through an exemplary situation of data transmissionin a WLAN, drawbacks of the current version of 802.11ax;

FIG. 7 shows a schematic representation a communication device inaccordance with embodiments of the present invention;

FIG. 8 shows a schematic representation of a wireless communicationdevice in accordance with embodiments of the present invention;

FIG. 9 a illustrates the impact of embodiments of the present inventionon the exemplary situation of FIG. 6 described above fornot-yet-associated stations in the process of associating with the AP;

FIG. 9 b illustrates an alternative to FIG. 9 a ;

FIG. 9 c illustrates another alternative to FIGS. 9 a and 9 b ;

FIG. 9 d illustrates a general embodiment in which a plurality ofdownlink resource units are allocated to multiple unassociated stations;

FIG. 10 a illustrates, using a flow chart, main steps at the accesspoint in relation with an MU Uplink transmission it triggers,implementing teachings of the present invention;

FIGS. 10 b and 10 c illustrate, using flow charts, main steps at theaccess point in relation with an MU Downlink transmission it triggerswhen implementing embodiments of the present invention;

FIG. 11 a illustrates, using a flow chart, main steps at an unassociatedstation in relation with an MU Uplink transmission triggered by anaccess point;

FIGS. 11 b and 11 c illustrate, using flow charts, main steps at anunassociated station in relation with an MU Downlink transmissiontriggered by an access point according to embodiments of the invention;

FIGS. 12 a and 12 b illustrate, through two exemplary situations of datatransmission in a WLAN, embodiments of the invention in which one MUDownlink resource unit is used by the AP to send data to unassociatedstations;

FIG. 13 a illustrates, using a flowchart, embodiments of the inventionimplemented at a physical access point when preparing and performing aMU Downlink transmission;

FIG. 13 b illustrates, using a flowchart, embodiments of the inventionimplemented at a non-AP station to handle RUs dedicated to groups ofstations in MU Downlink transmissions from the AP;

FIG. 14 illustrates the benefits of using group RUs with reference tothe exemplary situation of FIG. 6 described above;

FIG. 15 illustrates the benefits of using a newly proposed scheme foracknowledgment of a grouped multi-user downlink transmission;

FIG. 16 a illustrates, using a flowchart, an improvement of the processof FIG. 13 a (at the access point) to provide efficiently frameacknowledgment in case of group RUs;

FIG. 16 b illustrates, using a flowchart, an improvement of the processof FIG. 13 b (at a station) to perform efficient and immediate frameacknowledgment in case of group RUs; and

FIG. 17 shows an example format of an HE Capabilities element exchangedbetween a station and an AP;

FIGS. 18 a and 18 b illustrate, using flowcharts, steps performed,respectively, by an AP and a station when exchanging data;

FIG. 19 shows RU configuration examples between MU Downlink transmissionand MU Uplink transmission;

FIG. 20 illustrates, using a flowchart, an implementation exampleaccording to the invention taking into account the MSAS capabilitysubfield values advertised by stations; and

FIG. 21 illustrates, using a flowchart, an implementation exampleaccording to the invention taking into account the UMPS capabilitysubfield values advertised by unassociated stations..

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

FIG. 1 illustrates a communication system in which several communicationnodes (or stations) 101-107 exchange data frames over a radiotransmission channel 100 of a wireless local area network (WLAN), underthe management of a central station, or access point (AP) 110. The radiotransmission channel 100 is defined by an operating frequency bandconstituted by a single channel or a plurality of channels forming acomposite channel.

While the communication system of FIG. 1 shows a single physical accesspoint 110, the AP 110 may support multiple BSSs (also called set of“virtual APs”) and be configured to manage one or more WLANs (or BSSs),i.e. one or more groups of stations. Each BSS has to be uniquelyidentified by a specific basic service set identification, BSSID.

To achieve this configuration, the physical AP 110 may implement two (ormore) virtual APs to manage two (or more) WLANs, for instance: virtualAP 1 VAP-1 (not shown) having MAC address MAC1 as specific BSSID tomanage a first WLAN (BSS) with “guest” as SSID, and virtual AP 2 VAP-2(not shown) having MAC address MAC2 as specific BSSID to manage a secondWLAN (BSS) with “Employee” as SSID.

Some stations can register or “associate” with VAP-1 and thus join thefirst WLAN “guest”, while other stations can simultaneously registerwith VAP-2 and thus join the second WLAN “Employee”.

The security for each WLAN can be made different, i.e. WEP and WPA.

An AP device that supports multiple BSSIDs includes two types of virtualAPs. The first one is referred to as “transmitted AP” or “representativeAP”. Its BSSID is referred to as transmitted BSSID. It takes the primaryrole to transmit Multiple BSSID elements in beacon and probe responseframes. For a given physical AP, only one virtual AP is designated astransmitted AP.

The second type of virtual APs is referred to as “non-representative AP”or “non-transmitted AP”. Its BSSID is referred to as non-transmittedBSSID. The non-representative APs correspond to other virtual APs whichshall not broadcast beacon frames with Multiple BSSID elements. Howeverthey may broadcast beacon frames specific to its own BSS, i.e. withoutMultiple BSSID elements, in order to associate legacy STAs (stations notimplementing IEEE 802.11v) with itself.

The same physical device can join two WLANs simultaneously only if ithas two separate WLAN interfaces (e.g. Wi-Fi network cards). In thatcase, the device is considered as two stations in the network, eachstation being registered with only one WLAN at a time.

For the stations to be aware of available WLANs (or BSSs) and of theinformation defining them (for instance corresponding SSID or SSIDs,corresponding specific BSSID or BSSIDs, communication mode includingInfrastructure or Ad-Hoc, protection security schemes used includingOpen, WEP, WPA-PSK or 802.1X, support transmission rates used, channelin operation, and any optional Information Elements), the AP sends somecontrol or management frames, including beacon frames and probe responseframes which have substantially the same content.

A probe response frame is emitted by the AP to a specific station inresponse to a probe request frame broadcast by the station. This takesplace in an active discovery procedure where the station successivelyscans the 20 MHz channels and broadcast probe request frames therein. Inthe active discovery procedure, the station has to periodically remindits effective presence by sending new probe request frames.

On the other hand, a passive discovery procedure has been implementedwhere the AP voluntarily and periodically (e.g. each 100 ms) broadcastsa beacon frame to declare the WLAN to the stations.

Both beacon frames and probe response frames are used in any version of802.11, meaning that they are sent at lowest bit rate using a non-HT(high throughput) PPDU (Physical layer (PHY) Protocol Data Unit) formatas shown in FIG. 2 a .

This format is simple as it contains a preamble made of three fieldsthat can be understood by any station according to any version of802.11: L-STF (Legacy Short Training Field), L-LTF (Legacy Long TrainingField) and L-SIG (Legacy Signal Field) fields; followed by a Data fieldcontaining the payload data, here the information defining the WLAN todeclare.

The repetition of the probe request/response frames or of the beaconframes preempts a non-negligible part of network bandwidth. This partsubstantially increases with multiple WLANs that must share the samecommunication channels, and also with multiple physical APs (possiblysome implementing multiple BSSs), since multiple beacons are thusbroadcast (one for each active BSS).

As a consequence, the stations have to process beacon frames morefrequently and channel occupation due to management frames is increased.Increasing the beacon interval (to be more than 100 ms) so that thebeacon frame of each BSS is sent less frequently and the stationprocessing and channel occupation are reduced does not seem fullyrelevant. This is because the WLANs are less visible/detectable by thestations: some stations may not detect the beacon frame of a given BSSwhen scanning, and thus conclude a particular BSS (through its SSID) isnot available; also stations may decide to emit probe request frames tofind their networks, in an active manner, which thus results in havingprobe response frames broadcast by each neighborhood APs.

The discovery procedure (using beacon frames or probe response frames)may be the initial part of a more general association procedure duringwhich a station registers or associates with an AP to join acorresponding WLAN.

FIG. 3 illustrates an exemplary sequence of management frames allowing anot-yet-associated station to discover and register/associate with agiven Access Point. It comprises three phases: WLAN discovery,authentication and association, at the end of which the station entersinto an authenticated and associated state with the AP. Note that thestation may be currently associated with a first AP (i.e. belonging to afirst WLAN) and willing to join a second WLAN.

802.11 networks make use of a number of options for the first phase of802.11 probing or discovering. For instance, for an enterprisedeployment, the search for a specific network may involve sending aprobe request frame out on multiple channels that specifies the networkname (SSID) and bit rates.

More generally, prior to association with the AP, the stations gatherinformation about the APs by scanning the channels one by one eitherthrough passive scanning (passive discovery procedure introduced above)or active scanning (active discovery procedure introduced above).

In the passive scanning mode, the station scans through successivelyeach 20 MHz channel and waits to listen for beacon frames (declaringSSID) on the scanned channel, regardless of whether the stations hasalready connected to a specific SSID before or not.

In the active scanning mode, the stations send out probe request frames310 on each wireless 20 MHz channel. The probe request frames maycontain the SSID of a specific WLAN that the station is looking for orthe probe request frames may not contain a specific SSID meaning thestation is looking for “any” SSID in the vicinity of the station.

In response to receiving a probe request frame, the AP checks whetherthe station has at least one common supported data rate or not. If thereis a compatible data rate, the AP responds with a probe response frame320, the content of which is similar to a beacon frame: advertising ofthe SSID (wireless network name), of supported data rates, of encryptiontypes if required, and of other 802.11 capabilities of the AP.

An acknowledgment frame 330 may be sent by the station, in response toreceiving the probe response frame 320.

It is also common for a station that is already associated with an AP tosend probe request frames regularly onto other wireless channels tomaintain an updated list of available WLANs with best signal strengths.Thanks to this list, when the station can no longer maintain a strongconnection with the AP, it can roam to another AP with a better signalstrength using the second and third phases of the association procedure.

The second phase is the 802.11 authentication once a WLAN to join hasbeen chosen by the station. In particular, the station chooses acompatible WLAN from the probe response frames it receives.

802.11 was originally developed with two authentication mechanisms: thefirst authentication mechanism, called “open authentication”, isfundamentally a NULL authentication where the station says “authenticateme” and the AP responds with “yes”. This is the mechanism used in almostall 802.11 deployments; the second authentication mechanism, namely theWEP/WPA/WPA2, is a shared key mechanism that is widely used in homenetworks or small Wi-Fi deployments and provides security.

During the 802.11 authentication phase, the station sends a low-level802.11 authentication request frame 340 to the selected AP setting, forinstance, the authentication to open and a sequence to 0×0001. The APreceives the authentication request frame 340 and responds to thestation with an authentication response frame 350 set to open indicatinga sequence of 0×0002.

Note that some 802.11 capabilities allow a station to low-levelauthenticate to multiple APs without being associated with them (i.e.without belonging to corresponding WLANs). This speeds up the wholeassociation procedure when the station moves between APs. Indeed, whilea station can be 802.11 authenticated to multiple APs, it can only beactively associated and transferring data through a single AP at a time.

Next, the station has to perform actual association with the AP from thelow level authentication step. This is the next phase of actual 802.11association by which the station actually joins the WLAN cell. Thisstage finalizes the security and bit rate options and establishes thedata link between the station and the AP. The purpose of this finalexchange is for the station to obtain an Association Identifier (AID) tobe used to access the medium and send data within the joined WLAN.

Note that the station may have joined a first network and may roam fromone AP to another within the physical network. In that case, theassociation is called a re-association.

Once the station determines which AP (i.e. WLAN) it would like to beassociated with, the station sends an association request frame 360 tothe selected AP. The association request frame contains chosenencryption types if required and other compatible 802.11 capabilities.

If the elements in the association request frame match the capabilitiesof the AP, the AP creates an Association ID (AID) for the station andresponds with an association response frame 370 with a success messagegranting network access to the station.

Now the station is successfully associated with the AP, data transfercan begin in the chosen WLAN using the physical medium.

Note that when an AP receives a data frame from a station that isauthenticated but not yet associated, the AP responds with adisassociation frame placing the station into an authenticated butunassociated state. It results that the station must re-associate itselfwith the AP to join the corresponding WLAN.

The probe response frame 320, authentication request/response frames 340and 350 and association request/response frames 360 and 370 are unicastmanagement frames emitted in an 802.11 legacy format, known as a singleuser (SU) format. This is a format used for point-to-point communication(here between the AP and the station). Each of these unicast managementframes is acknowledged by an ACK frame 330.

As indicated above, all the management frames (310, 320, 340, 350, 360,370) and the ACK frames (330) use the lowest common rate supported byboth the station and the AP (e.g. 24mbps or less).

To meet the ever-increasing demand for faster wireless networks tosupport bandwidth-intensive applications, 802.11ac and later versions(802.11ax for instance) implement larger bandwidth transmission throughmulti-channel operations. FIG. 4 illustrates an 802.11ac channelallocation that supports composite channel bandwidth of 20 MHz, 40 MHz,80 MHz or 160 MHz.

IEEE 802.11ac introduced support of a restricted number of predefinedsubsets of 20 MHz channels to form the sole predefined composite channelconfigurations that are available for reservation by any 802.11ac (orlater) station on the wireless network to transmit data.

The predefined subsets are shown in the Figure and correspond to 20 MHz,40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHzand 40 MHz supported by 802.11n. Indeed, the 20 MHz component channels400-1 to 400-8 are concatenated to form wider communication compositechannels.

In the 802.11ac standard, the channels of each predefined 40 MHz, 80 MHzor 160 MHz subset are contiguous within the operating frequency band,i.e. no hole (missing channel) in the composite channel as ordered inthe operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels thatmay or may not be frequency contiguous. The 80 MHz and 40 MHz channelsare respectively composed of two frequency adjacent or contiguous 40 MHzand 20 MHz channels, respectively. However the present invention mayhave embodiments with either composition of the channel bandwidth, i.e.including only contiguous channels or formed of non-contiguous channelswithin the operating band.

A station (including the AP) is granted a transmission opportunity(TxOP) through the enhanced distributed channel access (EDCA) mechanismon the “primary channel” (400-3). Indeed, for each composite channelhaving a bandwidth, 802.11ac designates one channel as “primary” meaningthat it is used for contending for access to the composite channel. Theprimary 20 MHz channel is common to all stations (STAs) belonging to thesame BSS, i.e. managed by or registered with the same local Access Point(AP).

However, to make sure that no other legacy station (i.e. not belongingto the same set) uses the secondary channels, it is provided that thecontrol frames (e.g. RTS frame/CTS frame or trigger frame describedbelow) reserving the composite channel are duplicated over each 20 MHzchannel of such composite channel.

Transmissions in such composite channels is made from one station to theother (including the AP) using HE single user (SU) PPDU, the format ofwhich is shown in FIG. 2 b . It comprises, in addition to theconventional preamble (L-STF, L-LTF, L-SIG) readable by any legacystation, RL-SIG, HE-SIG-A, HE-STF, HE-LTF, Data and PE fields.

The IEEE 802.11ac standard enables up to four, or even eight, 20 MHzchannels to be bound. Because of the limited number of channels (19 inthe 5 GHz band in Europe), channel saturation becomes problematic.Indeed, in densely populated areas, the 5 GHz band will surely tend tosaturate even with a 20 or 40 MHz bandwidth usage per Wireless-LAN cell.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, one may consider multi-user (MU) transmissionfeatures, allowing multiple simultaneous transmissions to differentusers in both downlink (DL) and uplink (UL) directions, once atransmission opportunity has been reserved and granted to the AP. In theuplink, multi-user transmissions can be used to mitigate the collisionprobability by allowing multiple non-AP stations to simultaneouslytransmit to the AP.

To actually perform such multi-user transmission, it has been proposedto split a granted 20 MHz channel (400-1 to 400-4) into at least onesub-channel, but preferably into a plurality of sub-channels 310(elementary sub-channels), also referred to as sub-carriers or resourceunits (RUs) or “traffic channels”, that are shared in the frequencydomain by multiple users, based for instance on Orthogonal FrequencyDivision Multiple Access (OFDMA) technique.

This is illustrated with reference to FIG. 5 .

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent stations in order to increase competition within a reservedtransmission opportunity TXOP. This may help to reduce contention andcollisions inside 802.11 networks.

In this example, each 20 MHz channel (400-1, 400-2, 400-3 or 400-4) issub-divided in the frequency domain into four OFDMA sub-channels or RUs510 of size 5 MHz. Of course the number of RUs splitting a 20 MHzchannel may be different from four, and the RUs may have differentsizes. For instance, between two to nine RUs may be provided (thus eachhaving a size between 10 MHz and about 2 MHz). It is also possible tohave a RU width greater than 20 MHz, when included inside a widercomposite channel (e.g. 80 MHz).

Regarding the MU downlink transmission (from the AP to the stations),the AP can directly send multiple data to multiple stations in the RUs,by simply providing specific indications within the preamble header ofthe PPDU sent during the TXOP, and then sending data in the data field.RUs used in the downlink direction are known as downlink RUs, while RUsused in the uplink direction are known as uplink RUs.

FIG. 2 c illustrates the HE MU (Multi-User) PPDU format (HE-MU) used in802.11 ax for transmissions to one or more stations, in particular forMU downlink transmissions from AP to a plurality of stations.

The HE-MU PPDU includes the same preamble as the non-HT PPDU (FIG. 2 a )which is always transmitted at low bit rate. This is for all thedevices, especially the legacy ones not implementing 802.11ac/ax, to beable to understand the preamble for any of the transmission modes.

Since multiple stations are intended recipients or addressees of theOFDMA downlink transmissions, the AP needs to tell the stations in whichresource unit they will find their data. To achieve such signaling,802.1 1 ax provides the HE-SIG-B field 200 as shown in the Figure inwhich stations are assigned to RUs.

The SIG-B field 200 is only found in the downlink HE-MU-PPDU andcontains two types of fields as shown in FIG. 2 e : a single CommonBlock field 220 and one or more User Specific fields 230.

The single Common Block field 220 defines, through an RU allocationfield, the RU distribution for the current transmission opportunity (theother fields are of less importance). The format substantially followsthe same format as the downlink RU allocation provided in a TriggerFrame as introduced below.

802.11ax defines a set of predefined RU allocation schemes for 20 MHzchannels as shown in FIG. 2 f . The RU allocation field of Common Blockfield 220 thus references N 8-bit indexes pointing to entries of tableof FIG. 2 f .

Each such entry defines an RU allocation scheme, i.e. how the 20 MHzchannel is split into consecutive downlink RUs. The entry givesprecisely the position (according to frequency increasing order), thesize in terms of tones and the frequency range of each RU inside an MUtransmission.

For instance, the first entry (index=00000000) defines nine26-tone-width downlink RUs at positions #1 to #9. The frequency band ofdownlink RU at position #i is thus from the [26*(i-1)+1]^(th) tone tothe (26*i)^(th) tone of the considered 20 MHz channel. If the AP wantsto define a plurality of downlink RUs having this specific distribution,the RU allocation field of Common Block field 220 is set to value00000000.

The 12^(th) entry (index=00001011) of the table of predefined RUallocation schemes defines for instance a first 52-tone-width downlinkRU (position #1), followed by second, third and fourth downlink RUs witha 26-tones width (positions #2, #3 and #4), followed by fifth and sixthdownlink RUs with a 52-tones width (position #5 and #6).

The User Specific fields 230 define information related to each downlinkRU defined in the Common Block field, and are provided in the same orderas the downlink RUs are successively defined in the Common Block field.For instance, the n^(th) declared User Specific field 230 givesinformation about the n^(th) downlink RU as defined in the Common Blockfield, i.e. downlink RU at position #n.

Each User Specific field 230 includes the AID of the addressee station(‘STA-lD’ field; provided by the AP during the association procedure ofFIG. 3 ), and also other information such as modulation and codingschemes, spatial streams, etc., which are of less importance here.

As only a single downlink RU can be allocated to a given station, thesignaling that enables a station to decode its data is carried in onlyone User Specific field (corresponding to the single RU).

Based on the resource distribution provided in the Common Block fieldand each corresponding User Specific field, a station can easily knowwhich resource unit has been allocated to it and thus in which downlinkRU it will receive its data from the AP.

The HE-SIG-B is encoded on a per-20 MHz basis using BCC and is sent onthe station’s preferred band so that the station’s signaling informationis sent on the same band as the payload.

Things are different for the MU uplink transmissions, because the APmust control when and how (in which RU) the stations must emit data.

Contrary to the MU downlink transmission, a trigger mechanism has beenadopted for the AP to trigger MU uplink communications from variousnon-AP stations. This is for the AP to have such control on thestations.

To support a MU uplink transmission (during a TXOP pre-empted by theAP), the 802.11ax AP has to provide signalling information for bothlegacy stations (i.e. non-802.11ax stations) to set their NAV and for802.11ax stations to determine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11axstations, meaning 802.11 stations of previous technologies that do notsupport OFDMA communications.

As shown in the example of FIG. 5 , the AP sends a trigger frame (TF)530 to the targeted 802.11ax stations to reserve a transmissionopportunity. The bandwidth or width of the targeted composite channelfor the transmission opportunity is signalled in the TF frame, meaningthat the 20, 40, 80 or 160 MHz value is signalled.

The TF frame is a control frame, according to the 802.11 legacy non-HTformat shown in FIG. 2 a , and is sent over the primary 20 MHz channeland duplicated (replicated) on each other 20 MHz channels forming thetargeted composite channel. Due to the duplication of the controlframes, it is expected that every nearby legacy station (non-HT or802.11ac stations) receiving the TF on its primary channel, then setsits NAV to the value specified in the header of the TF frame. Thisprevents these legacy stations from accessing the channels of thetargeted composite channel during the TXOP.

Based on an AP’s decision, the trigger frame TF may define a pluralityof uplink resource units (RUs) 510. The multi-user feature of OFDMAallows the AP to assign different RUs to different stations in order toincrease competition. This may help to reduce contention and collisionsinside 802.11 networks.

The information about the RU distribution in the requested transmissionopportunity and about the assignment of stations to the uplink RUs isindicated in the payload of the MAC frame carried in the Data field(shown in FIG. 2 a ). Indeed, the MAC payload is basically empty forclassical control frames (such as RTS or CTS frame), but is enhancedwith an information structure for Trigger Frames: an RU allocation fielddefines the allocated uplink RUs (i.e. RU distribution in the TXOP)while one or more User Info fields indicates the information related toeach respective uplink RU (in the same order as provided by the RUallocation info field). In particular, the Address field in each UserInfo field provides the AID of the station to which the correspondinguplink RU is assigned.

These various fields are similar to those (Common Block and UserSpecific) defined above with reference to FIGS. 2 e and 2 f .

The trigger frame 530 may define “Scheduled” uplink RUs, which may bereserved by the AP for certain stations in which case no contention foraccessing such RUs is needed for these stations. Such scheduled RUs andtheir corresponding scheduled stations are indicated in the triggerframe (the Address field of the User Info field for the scheduled RU isset to the AID of the station). This explicitly indicates the stationthat is allowed to use each Scheduled RU. Such transmission modecompetes with the conventional EDCA mechanism within the station toaccess the medium.

If a station finds that there is no User Info field for Scheduled RUs inthe Trigger frame 530 carrying its AID in the Address field, then thestation should not be allowed to transmit in a Scheduled RU of the TXOPtriggered by the TF.

The trigger frame TF 530 may also designate “Random” uplink RUs (alsoreferred to as “Random Access” (RA) RUs), in addition or in replacementof the “Scheduled” RUs. The Random RUs can be randomly accessed bystations. In other words, Random RUs designated or allocated by the APin the TF may serve as basis for contention between stations willing toaccess the communication medium for sending data. A collision occurswhen two or more stations attempt to transmit at the same time over thesame random RU.

Such random RUs are signalled in the TF by using specific reserved AIDin the Address field of the User Info field corresponding to the RU. Forinstance, an AID equal to 0 is used to identify random RUs available forcontention by stations associated with the AP emitting the trigger frame(i.e. belonging to the same BSS). On the other hand, an AID equal to2045 may be used to identify random uplink RUs available for contentionby not-yet-associated or “associated” stations (i.e. not belonging tothe same BSS as the AP sending the TF 530).

Note that several random RUs with AID=0 and/or with AID=2045 may beprovided by the same TF.

A random allocation procedure may be considered for 802.11ax standardbased on an additional backoff counter (OFDMA backoff counter, or OBOcounter or RU counter) for random RU contention by the 802.11ax non-APstations, i.e. to allow them performing contention between them toaccess and send data over a Random RU. The RU backoff counter isdistinct from the classical EDCA backoff counters (as defined in 802.11eversion). However data transmitted in an accessed OFDMA RUs 510 isassumed to be served from same EDCA traffic queues.

The RU random allocation procedure comprises, for a station of aplurality of 802.11ax stations having a positive RU backoff value(initially drawn inside an RU contention window range), a first step ofdetermining, from a received trigger frame, the sub-channels or RUs ofthe communication medium available for contention (the so-called “randomRUs”, either identified by a value 0 for already-associated stations ora value 2045 for unassociated stations), a second step of verifying ifthe value of the RU backoff value local to the considered station is notgreater than the number of detected-as-available random RUs, and then,in case of successful verification, a third step of randomly selecting aRU among the detected-as-available RUs to then send data. In case thesecond step is not verified, a fourth step (instead of the third) isperformed in order to decrement the RU backoff counter by the number ofdetected-as-available random RUs.

As one can note, a station having no Scheduled RU is not guaranteed toperform OFDMA transmission over a random RU for each TF received. Thisis because at least the RU backoff counter is decremented upon eachreception of a Trigger Frame by the number of proposed Random RUs,thereby deferring data transmission to a subsequent trigger frame(depending of the current value of the RU backoff number and of thenumber of random RUs offered by each of further received TFs).

Back to FIG. 5 , it results from the various possible accesses to theuplink RUs that some of them are not used (510u) because no station withan RU backoff value less than the number of available random RUs hasrandomly selected one of these random RUs, whereas some other uplink RUshave collided (as example 510 c) because at least two of these stationshave randomly selected the same random RU. This shows that due to therandom determination of random RUs to access, collision may occur oversome uplink RUs, while other RUs may remain free.

The Uplink transmission of data by the stations in the RUs 510 is madeusing HE Trigger-Based PPDUs (HE_Trig) as shown in FIG. 2 d in eachuplink RU accessed by the stations. Each HE-Trig PPDU carries a singletransmission (i.e. from one station to the AP) in response to thetrigger frame 530. This HE-Trig PPDU frame format has a format quitesimilar to the one of HE SU PPDU, except the duration of the HE-STFfield is 8 µs.

Once the stations have used the Scheduled and/or Random RUs to transmitdata to the AP, the AP responds with a Multi-User acknowledgment (notshown in FIG. 5 ) to acknowledge the data received on each uplink RU.

FIG. 2 g illustrates a typical format of a MAC frame 230 that may becarried in the Data field of the different PPDUs as shown in FIGS. 2 a-2d , i.e. either in downlink direction by the AP or in uplink directionby the stations.

The illustrated MAC frame contains 24 octets of MAC header, 0 to 2312octets of Frame Body 207, and 4 octets of Frame Check Sequence (FCS)208. The MAC header includes among other fields: a frame control field201, a duration field 202, a RA (Receiver or Destination Address) field203 and a TA (Transmitter or Source Address) field 204.

In downlink direction for instance, the RA field 203 is set to the MACaddress of the station to be destined (unicast MAC address) or to thebroadcast value FF:FF:FF:FF:FF:FF if the MAC frame is destined to allstations (broadcast MAC address). The Frame Body is a field of variablelength and e.g. its information may be a frame exchanged during theassociation process (e.g. as described below with reference to FIG. 6 ).For example, the MAC frame body 207 may encapsulate management framessent by the AP during the association procedure (as explained above withreference to FIG. 3 ). The control field 201 in this case indicates thatthe MAC frame is a management frame.

In this disclosure a MAC frame and MAC Protocol Data Unit (MPDU) aresynonyms and define the unit of data exchanged between MAC entities. Anaggregate MAC PDU (A-MPDU) is a structure that contains one or moreMPDUs and is transported in PHY Protocol Data Unit (PPDU). An A-MPDU mayfor example be carried in an HE SU PPDU, an HE MU PPDU or an HEtrigger-based PPDU.

FIG. 6 illustrates, through an exemplary situation of data transmissionin a WLAN, drawbacks of the current version of 802.11ax.

In this exemplary situation, the wireless network comprising a physicalaccess point 110 and a plurality of associated stations STA2, STA3,STA4, STA5, STA7 and STA8 and a plurality of unassociated 802.11axstations STA1 and STA6.

The AP 110 emits periodically a beacon frame 610, containing parametersof WLAN/BSS group(s).

All stations (including the AP) contend for an access to the wirelessnetwork using conventional EDCA scheme. The contention process (backoffcounters) at each station starts or restarts each time the wirelessnetwork is detected as idle for a predefined time period (usually DIFStime period after the end of a previous TXOP, for instance after anacknowledgment from the AP or after end of a PPDU transmission).

When accessing to the medium, the AP 110 sends a trigger frame 530 toreserve a MU UL transmission opportunity (TXOP#1) on at least onecommunication channel of the wireless network. The trigger frame 530defines resource units for the MU Uplink OFDMA transmission in TXOP#1,including one or more random RUs associated with AID=2045 (i.e.dedicated or reserved or assigned to unassociated stations like STA1 andSTA6). This is for the not-yet-associated stations to speed up theirassociation procedure, while reducing medium access and occupancy. Inthe example, two random RUs with AID=2045 are provided, the other RUsbeing Scheduled RUs and/or random RUs with AID=0 (i.e. dedicated orreserved or assigned to already-associated stations like STA2, STA3,STA4, STA5, STA7 and STA8).

In response to the TF 530, the AP receives data on the uplink RUs 510from one or more stations during the MU Uplink OFDMA transmission time.This includes data transmitted over Scheduled RUs but also over RandomRUs.

In particular, the AP may receive request management frames (e.g. 310,340, 360) from not-yet-associated 802.11ax stations such as STA1 andSTA6, over the Random RUs with AID=2045.

Upon receiving the data and management frames over the uplink RUs 510forming the MU Uplink OFDMA transmission, the AP 110 responds with aMulti-STA BlockAck Frame 640 using a HE SU PPDU (having a “receivingaddress” RA field of the encapsulated MAC frame set with a broadcastaddress). Note that the AP acknowledges receipt to each sending stationby providing, in the Multi-STA BlockAck Frame, the AID of the sendingstation for which data have been correctly received. As no AID has beenassociated with each not-yet-associated station, the Multi-STA BlockAckFrame is modified to receive the MAC address of each not-yet-associatedstation for which the requested management frame has been correctlyreceived.

Next to TXOP#1, the AP 110 may again gain access to the medium for a newTXOP, referred to as TXOP#2, to perform a MU Downlink OFDMA transmission620.

Several issues arise from this exemplary scenario, which are solved byseveral embodiments described below.

FIG. 7 schematically illustrates a communication device 700, either anon-AP station 101-107 or the access point 110, of the radio network100, configured to implement at least one embodiment of the presentinvention. The communication device 700 may preferably be a device suchas a micro-computer, a workstation or a light portable device. Thecommunication device 700 comprises a communication bus 713 to whichthere are preferably connected:

-   a central processing unit 711, such as a microprocessor, denoted    CPU;-   a read only memory 707, denoted ROM, for storing computer programs    for implementing the invention;-   a random access memory 712, denoted RAM, for storing the executable    code of methods according to embodiments of the invention as well as    the registers adapted to record variables and parameters necessary    for implementing methods according to embodiments of the invention;    and-   at least one communication interface 702 connected to the radio    communication network 100 over which digital data packets or frames    or control frames are transmitted, for example a wireless    communication network according to the 802.11ax protocol. The frames    are written from a FIFO sending memory in RAM 712 to the network    interface for transmission or are read from the network interface    for reception and writing into a FIFO receiving memory in RAM 712    under the control of a software application running in the CPU 711.

Optionally, communication device 700 may also include the followingcomponents:

-   a data storage means 704 such as a hard disk, for storing computer    programs for implementing methods according to one or more    embodiments of the invention;-   a disk drive 705 for a disk 706, the disk drive being adapted to    read data from the disk 706 or to write data onto said disk;-   a screen 709 for displaying decoded data and/or serving as a    graphical interface with the user, by means of a keyboard 710 or any    other pointing means.

The communication device 700 may be optionally connected to variousperipherals, such as for example a digital camera 708, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 700.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 700 or connected to it. The representation of thebus is not limiting and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 700 directly or by means of another element of the communicationdevice 700.

The disk 706 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to the invention to be implemented.

The executable code may optionally be stored either in read only memory707, on the hard disk 704 or on a removable digital medium such as forexample a disk 706 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 703, via the interface 702, in order to bestored in one of the storage means of the communication device 700, suchas the hard disk 704, before being executed.

The central processing unit 711 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 704 or in the read only memory 707, aretransferred into the random access memory 712, which then contains theexecutable code of the program or programs, as well as registers forstoring the variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 8 is a block diagram schematically illustrating the architecture ofthe communication device 700, either the AP 110 or one of stations101-107, adapted to carry out, at least partially, the invention. Asillustrated, device 700 comprises a physical (PHY) layer block 803, aMAC layer block 802, and an application layer block 801.

The PHY layer block 803 (here an 802.11 standardized PHY layer) has thetask of formatting, modulating on or demodulating from any 20 MHzchannel or the composite channel, and thus sending or receiving framesover the radio medium used 100, such as 802.11 frames, for instancemedium access trigger frames TF 530 (FIG. 5 ) to reserve a transmissionslot, MAC data and management frames based on a 20 MHz width to interactwith legacy 802.11 stations, as well as of MAC data frames of OFDMA typehaving smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/fromthat radio medium.

The MAC layer block or controller 802 preferably comprises a MAC 802.11layer 804 implementing conventional 802.11ax MAC operations. The MAClayer block 802 may optionally be implemented in software, whichsoftware is loaded into RAM 712 and executed by CPU 711.

The device 700 further comprises an additional block 805 implementingthe part of embodiments of the invention (either from stationperspective or from AP perspective). The additional block 805 may beimplemented at the MAC layer block 802 and/or the physical layer block803, and thus may interact with both blocks. In one implementation, theadditional block 805 receives formed MAC frames for encapsulation in MUDL frames.

MAC 802.11 layer 804, additional block 805 and PHY layer block 803interact one with the other in order to process accuratelycommunications over OFDMA according to embodiments of the invention.

On top of the Figure, application layer block 801 runs an applicationthat generates and receives data packets, for example data packets of avideo stream. Application layer block 801 represents all the stacklayers above MAC layer according to ISO standardization.

Back to the several issues arisen from the scenario of FIG. 6 , the RUsprovided for the MU Downlink OFDMA transmission are assigned to specificstations using their AID. In the example shown, the RUs are successivelyassigned to STA3, STA5, STA4, STA2, STA8 and STA7.

For some stations, here STA3 and ST8, the amount of data to transmit issmall regarding the size of the reserved RU. As a consequence, paddingdata (black portions) are added by the AP 110 to keep sufficientactivity on the 20 MHz channel (for detection by legacy nodes in orderto avoid unexpected access). The black portions of the RUs shown in theFigure illustrate how the padding wastes bandwidth of the network.

The AP 110 may also have received a multicast MAC frame from anothernetwork or from upper OSI layer, to be addressed to a plurality ofaddressee stations, here STA4 and STA5.

Multicast addressing can be used in the link layer, such as Ethernetmulticast, and at the Internet layer (as example, IP protocol includesthe addresses from 224.0.0.0 to 239.255.255.255 as a multicast range).

As 802.11ax does not provide any mechanism to allow multicast traffic ina MU Downlink OFDMA transmission, the AP has to duplicate the MAC frameinto two HE-MU PPDUs to be transmitted over two separate RUs as shown inthe Figure for the RUs assigned to STA5 and STA4. This also wastesbandwidth, in particular because of the costs of signalling two separateRUs.

Acknowledgment of the data frames sent during the MU Downlink OFDMAtransmission may be performed by the receiving stations STA2-5 andSTA7-8 during an MU ACK period 625 belonging to the same TXOP#2. MU ACKperiod 625 is for instance a subsequent MU Uplink OFDMA transmissionimmediately following the MU Downlink OFDMA transmission.

As such, MU ACK period 625 is made of a plurality of scheduled RUs (herebelow named “response” or “acknowledgement” or “ack” RU) which aredefined in a dedicated MAC header portion of frames conveyed in thepreceding MU Downlink OFDMA transmission.

The response RU to be used by each one of receiving stations STA2-5 andSTA7-8 in MU ACK period 625 for frame acknowledgment is identified inresponse resource unit information provided by the AP in the sent dataframes of the MU Downlink OFDMA transmission. Thanks to thisidentification, the response RUs are (indirectly) assigned to stations.The response RUs are thus scheduled RUs. Usually, the response RU is thesame (i.e. same RU position) as the one used during MU Downlink OFDMAtransmission.

The response resource unit information is signalled in a so-calledUplink Multi-user Response Scheduling (or UMRS) control subfield withinone (or more) of the data frames addressed to the receiving station.

The UMRS subfield is defined in the 802.11ax, version 2.0, standard asdescribed now with reference to FIGS. 2 h to 2 j .

FIG. 2 h illustrates a MAC header of a MAC frame within an HE Multi-userPPDU conveyed over a MU DL transmission 620. The MAC frame (and thus MACheader) is conveyed in the Data field of an HE MU PPDU (see FIG. 2 c ).

As known, the MAC header includes a field “Address_1” 210 containing theReceive Address (RA) of the MAC frame, that is to say the MAC address ofthe addressee station to which the MPDU is addressed. In a particularcase, the MAC address may be a broadcast address (e.g.FF:FF:FF:FF:FF:FF). This MAC header also includes an HT Control field250. The latter can take several configurations depending on the 802.11standard considered. The HE variant configuration corresponds to 802.11ax standard, in which case the HE variant HT Control field comprises anA-Control subfield 260 (standing for Aggregated Control fields) shown inFIG. 2 i .

The A-Control subfield 260 aggregates several control fields, which is asequence of one or more Control subfields 261. The length of theA-Control subfield 260 is equal to 30 bits. Each Control subfield 261 iscomposed of a Control ID 262 subfield indicating the type of informationcarried in the Control Information subfield 263 that follows. Paddingbits are added to reach a 30-bit A-Control subfield if necessary.

Various type of information may thus be provided through the A-Controlsubfield 260. For instance, operating mode may be indicated in ControlInformation subfield 263 when Control ID 262 is 1. Also, power data maybe indicated in Control Information subfield 263 when Control ID 262 is4.

When Control ID 262 is 0, Control Information subfield 263 is an UL MUresponse scheduling (UMRS) information or Control subfield 264. Arepresentation of the UMRS information 264 is shown in FIG. 2 j . Itcomprises various subfields over 26 bits.

One of them is the 8-bit RU Allocation subfield 265. It indicates whichresponse RU of MU Ack 625 to be used by the addressee station receivingthe corresponding HE Multi-user MPDU to provide a response (HETriggered-based PPDU, as shown in FIG. 2 d ) to the data frames to theaccess point.

The format of RU Allocation subfield 265 substantially follows the sameformat as the RU Allocation subfield provided in Common Block 220 ofHE-SIG-B field 200 or the RU Allocation subfield provided in a TriggerFrame as introduced above.

One can note the UMRS information 264 does not need a subfield toindicate the AID of the station intended to emit the response, as thisstation is the addressee station receiving the HE DL MU frame containingthe UMRS information 264 (i.e. the station to which the RU has beenassigned).

If no valid UMRS information 264 is found, the addressee station shallnot respond to the access point.

Usually, only one MPDU sent by the AP over the same RU includes the UMRSinformation 264. Of course, several MPDUs can include such information,in which case the UMRS Control fields 264 within MPDUs carried in anA-MPDU have the same value, i.e. all the occurrences of the UMRSinformation have the same value: The UMRS Control fields within MPDUscarried in an A-MPDU have the same value. This is to avoid conflict whendetermining the response RU to be used.

Back to FIG. 6 , as the AP must assign an AID to a downlink RU of the MUDownlink OFDMA transmission, the AP cannot use the MU Downlink OFDMAtransmission to provide response management frames (e.g. 320, 350, 370)to the unassociated stations, here STA1 and STA6. In the current versionof 802.11ax, the MU Downlink OFDMA transmission is restricted toalready-associated stations. It means that the response managementframes (from the AP to the stations) are still to be conveyed using thelegacy single user (SU) mode: for instance, the AP 110 waits untilaccessing again the medium for a new TXOP (here TXOP#3), during whichthe AP 110 sends for instance a probe response frame 320 to STA1 usingan HE SU PPDU 630-1; and waits again until accessing again the mediumfor another TXOP (here TXOP#4), during which the AP 110 sends forinstance an authentication response frame 350 to STA6 using an HE SUPPDU 630-2. In all cases, an acknowledgment ACK 330 may be received fromthe addressee station.

The need to use HE SU PPDUs for handling the response management framesis not satisfactory: on one hand, it introduces delays in the networkmanagement because the AP 110 has to contend for new accesses to thenetwork; on the other hand, it inefficiently uses the medium for a longtime, given the few data to be transmitted, because the HE SU PPDUs aresend at low bit rate.

These various drawbacks of the current version of 802.11ax (illustratedthrough an exemplary situation of exchange of management frames, butwhich may concern any other type of frames) show that a more efficientusage of the MU Downlink transmission is sought.

A first approach to solve part of these drawbacks is introduced belowand described with exemplary detailed embodiments with reference toFIGS. 9 a-d to 12 a-b .

Other approaches, based on aggregation, that also solve part of thesedrawbacks are introduced further below and described with exemplarydetailed embodiments with reference to FIGS. 13 a-b to 16 .

According to the first approach, the inventors have contemplatedallowing downlink RUs in the MU Downlink transmission to be addressed(assigned) to stations without using AIDs, for instance to stationsdeprived of AIDs such as unassociated stations.

A first novel idea relies on using a specific AID which has not beenassociated with a specific station when registering/associating, forinstance an association identifier reserved for stations not associatedwith the access point such as AID=2045.

Thus, an AP willing to address stations having no AID may provide aplurality of downlink resource units in a multi-user downlinktransmission from the access point within a transmission opportunitygranted to the access point, wherein the plurality of downlink resourceunits comprises a downlink resource unit assigned to an associationidentifier not associated with a specific station (e.g. reserved forstations not associated with the access point). Next, the AP may send aframe to a station on such a downlink resource unit reserved forstations not associated with the access point.

It makes it possible for the addressee station or stations to simplydetermine a downlink resource unit assigned to an association identifiernot associated with a specific station (e.g. reserved for stations notassociated with the access point such as AID=2045), from a plurality ofdownlink resource units comprised in a multi-user downlink transmissionfrom the access point within a transmission opportunity granted to theaccess point. Next, the station may receive a frame from the accesspoint on the determined downlink resource unit.

A second novel idea relies on a matching in terms of RU profile betweenan uplink RU already used by a station in the MU Uplink transmission anda downlink RU the AP will use in the MU Downlink transmission to providea frame to the same station.

Thus, when the station sends (or conversely the AP received) a frame(e.g. a request management frame of a not-yet-associated station) to theaccess point using an uplink resource unit of a plurality of uplinkresource units provided in a multi-user uplink transmission towards theaccess point within a transmission opportunity granted to the accesspoint, wherein the plurality of uplink resource units are distributedaccording to an allocation scheme (e.g. frequency-distributed), the APmay build a plurality of downlink resource units comprised in amulti-user downlink transmission from the access point within the sameor a next transmission opportunity granted to the access point, theplurality of downlink resource units comprising a downlink resource unithaving at least one matching allocation scheme feature with the uplinkresource unit, and then send a frame (e.g. a response management frame)to the station on the downlink resource unit.

In this context, the station only has to determine the downlink resourceunit, based on the allocation scheme feature of the uplink resource unitit has used, and then receives the frame from the access point on thedetermined downlink resource unit.

In embodiments, such determination by the station may depend on thenumber of downlink resource units assigned to the association identifiernot associated with a specific station (e.g. reserved for stations notassociated with the access point), in the multi-user downlinktransmission. This is to provide the ability for the stations to switchbetween two behaviors.

For example, if only one downlink RU with a predefined identifierreserved for unassociated stations (e.g. AID=2045) is contained in a MUdownlink transmission, each unassociated station may be considered asrecipient of the downlink RU, i.e. the downlink RU may potentiallycontain a frame addressed to that station. For instance, the downlink RUmay contain a frame for one of the unassociated stations or contain abroadcast frame for all unassociated stations. In this behaviour, theallocation scheme of the MU uplink transmission is not taken intoaccount.

Each recipient station may check the RA field (receiver or destinationaddress) of the (MAC) frame(s) contained in that downlink RU in order tokeep (“receive”) only that(those) for which the station is theaddressee.

On the other hand, if more than one downlink RU with a predefinedidentifier reserved for unassociated stations (e.g. AID=2045) iscontained in a MU downlink transmission, an unassociated station has todetermine its assigned downlink resource unit, if any, based on theallocation scheme feature of the uplink resource unit it has used. Ifsuch downlink RU matching the allocation scheme feature is found, theunassociated station receives the frame from the access point on thatdetermined downlink resource unit.

In that case, each downlink RU has only one recipient station. Thus, theunassociated station may optionally check the RA field of the (MAC)frame(s) contained in that downlink RU to confirm that the frames areindeed addressed to it.

Even when implementing the checking step, the unassociated station takesbenefit from the uplink signalling to determine which downlink RU todecode. Advantageously, in either cases (one downlink RU or a pluralityof downlink RUs not assigned to a specific station), each unassociatedstation does not have to decode more than one downlink RU.

Thus, an unassociated non-AP station that receives a MU DL frame (e.g.an HE MU PPDU) containing RUs with the STA-ID equal to 2045, shall beconsidered as the recipient of a RU with the STA-ID equal to 2045 if oneof the following conditions occurs:

-   There is only one RU with the STA-ID equal to 2045 in the MU DL    frame; and-   The STA has previously sent a management request frame in response    to a Trigger frame containing Random Access-RU(s) with AID set to    2045, and the RU with STA-ID equal to 2045 has the same RU    allocation as the RU allocation of the RA RU carrying the request in    the previously sent MU UL frame (e.g. an HE TB PPDU according to    802.11 ax).

Note that a MU DL RU with AID=2045 may also be referred to as a“broadcast RU”. With this naming, a broadcast RU may contain a unicastMAC frame (RA field corresponding to a unicast MAC address) or abroadcast MAC frame (RA field corresponding to a broadcast MAC address).

Note also that providing multiple RUs with the STA-ID equal to 2045 inan HE MU PPDU may be viewed as an exception to a general requirement ofnot having more than one downlink RU addressed to an associated STA. Inother words, if the list of STAs that are recipients of the transmittedHE MU PPDU are represented by an array STA_ID_LIST, a STA_ID_LISTelement with a particular (AID) value shall not appear more than once inthe array except if:

-   the value identifies an unallocated RU (e.g. 2046); or-   the value is 2045, which identifies a broadcast RU destined to an    unassociated STA.

According to embodiments, and from the AP perspective, the AP sends toan unassociated STA an association response frame in a broadcast RU(e.g. with AID=2045) considering the following constraints:

-   multiple broadcast RUs (AID=2045) may be inserted in a HE MU PPDU;-   if only one broadcast RU (AID=2045) is inserted in a HE MU PPDU, the    broadcast RU can be addressed to one or all unassociated STAs;-   if multiple broadcast RUs (AID=2045) are inserted in a HE MU PPDU,    each broadcast RU is addressed to only one unassociated STA;-   to send an association response frame to an unassociated STA;    -   the AP may use the same RU allocation for the broadcast RU        (AID=2045) as the RU allocation of the RA RU (AID=2045) used by        the unassociated STA to send the corresponding association        request frame (cf. FIG. 9 d );    -   the AP may use a single broadcast RU (AID=2045) embedding a        broadcast MAC frame to broadcast an association response frame        to all unassociated STAs (cf. FIG. 12 a ); or    -   the AP may use a single broadcast RU (AID=2045) embedding a        unicast MAC frame addressed to the unassociated STA (cf. FIG. 12        b ).

A broadcast RU containing a unicast MAC frame addressed to anunassociated station may include an information item identifying anuplink resource unit to be used by the unassociated station in amulti-user uplink transmission opportunity following the multi-userdownlink transmission opportunity to provide an acknowledgement to theaccess point. The UMRS control field as defined in draft 2.1 of standardIEEE 802.11ax may be used to indicate which UL RU must be used by theunassociated STA to acknowledge the MPDU.

It results from these ideas that MU Downlink transmission can beefficiently extended to unassociated stations, and more generally to anystations without using an AID assigned to a specific station. Preferablyan AID reserved for stations not associated with the access point isused.

MU Downlink transmission is thus significantly improved compared toknown current 802.11 ax requirements.

For these novel ideas, the additional block 805 may act as an RU profilemanagement module for controlling usage of Downlink OFDMA resource units(sub-channels).

For instance and not exhaustively, the operations for the AP may includedetermining an uplink RU used by a station in MU Uplink transmission forwhich no AID is available (e.g. an AID reserved for unassociatedstations), storing RU allocation scheme features related to the useduplink RU, building an MU Downlink transmission with downlink RUsincluding a downlink RU that matches the stored RU allocation schemefeatures and sending a response to the station within such matchingdownlink RU. The operations for a station different from the AP mayinclude keeping track of RU allocation scheme features of an uplink RUused to transmit data (e.g. request) to the AP in MU Uplinktransmission, determining a downlink RU in MU Downlink transmission thatmatches the RU allocation scheme features of the RU used in order toread the response provided by the AP on this matching downlink RU.

In that case, MAC 802.11 layer 804, RU Profile management module 805 andPHY layer block 803 interact one with the other in order to processaccurately communications over Downlink OFDMA RU addressed to a stationwithout using an AID associated with said station.

Embodiments of these ideas are now illustrated using various exemplaryembodiments in the context of IEEE 802.11ax by considering OFDMA RUs.

Although the proposed examples are also mainly described with referenceto the management frames of the 802.11 association process, the firstapproach is not limited to such management frame transmission but mayapply to any 802.11 data or control frame.

FIG. 9 a illustrates the impact of some embodiments of the firstapproach on the exemplary situation of FIG. 6 described above fornot-yet-associated stations STA1 and STA6 in the process of associatingwith the AP.

The AP 110 is granted TXOP#1 and sends the same trigger frame 530 as inFIG. 6 to reserve a MU UL transmission opportunity. This trigger frame530 defines at least one random RU with AID=2045 (here two such randomRUs). Not-yet-associated stations STA1 and STA6 send request managementframes to the AP in the random RUs 510 with AID=2045 (the other RUs areused by other stations).

The AP acknowledges the received frames using a Multi-STA BlockAck frame640.

During this sequence, both AP and stations perform specific operationsin order to save one or more allocation scheme features that define theuplink RUs used by STA1 and STA6.

This includes one or more of the following information: a position ofthe uplink resource unit in the allocation scheme used (i.e. in thecorresponding entry of FIG. 2 f ); a frequency band of the uplinkresource unit in the allocation scheme used (i.e. which tones in the 20MHz channel according to the corresponding entry of FIG. 2 f ); a sizeof the uplink resource unit in the allocation scheme used (i.e. in thenumber of tones as shown in the corresponding entry of FIG. 2 f ).

For instance, FIG. 10 a illustrates, using a flow chart, main steps atthe AP in relation with an MU Uplink transmission it triggers.

At step 1010, the MU Uplink transmission is initiated with trigger frame530.

If the AP receives a frame from a not-yet-associated station on a randomRU with AID=2045 (test 1020), the AP stores the RU profile, i.e.relevant allocation scheme features, of the uplink RUs used andassociates each of them with the transmitted not-yet-associated station,at step 1030. The frame is for example a request management frame.

For instance, the AP may store the MAC address of the not-yet-associatedstation (which is obtained in the request management frame received)together with the 8-bit index corresponding to the allocation schemeused (FIG. 2 f ) and the position of the uplink RU used from amongst thelist defined by the allocation scheme used. These three items ofinformation make it possible for the AP to retrieve any of theabove-mentioned allocation scheme features.

In case of negative test 1020, the algorithm loops back to step 1010,waiting for the transmission of a new trigger frame.

Next to step 1030, the AP sends, at step 1040, acknowledgments to thetransmitting stations, including the not-yet-associated stations havingsent e.g. request management frames.

Correspondingly, FIG. 11 a illustrates, using a flow chart, main stepsat a not-yet-associated station in relation with an MU Uplinktransmission triggered by the AP.

The process starts at step 1110 where the not-yet-associated stationdetects a trigger frame 530 sent by the AP, that includes one or morerandom RUs with AID=2045.

In that case, the not-yet-associated station willing toregister/associate with the AP contends for access to such a random RUswith AID=2045. When such a random RU is granted to thenot-yet-associated station, the latter transmits a request frame such asa request management frame (310, 340, 360 depending on which phase ofthe association procedure the station is entering) in the accessedrandom RU 510 with AID=2045. This is step 1120.

If an acknowledgment is received from the AP (test 1130) meaning thatthe AP will respond to the request in the future, the not-yet-associatedstation stores the RU profile, i.e. relevant allocation scheme features,of the random RUs used. This is step 1140.

For instance, the not-yet-associated station may store the 8-bit indexcorresponding to the allocation scheme used (FIG. 2 f ) and the positionof the uplink RU used from amongst the list defined by the allocationscheme used.

Turning back to FIG. 9 a , the AP initiates a MU Downlink transmissionin the same TXOP#1. This is possible thanks to the cascading optionprovided by 802.11ax (the AP may enable a cascading field in the headerof trigger frame 530 in order to warn the stations that it will cascadeseveral MU transmissions, either Downlink or Uplink, during the grantedTXOP). Alternatively, after the Multi-STA BlockAck frame 640, the AP maypreempt the medium by waiting less than the DIFS period (the otherstation will thus no have time to start decrementing their backoffcounter to contend for access to the medium).

In this example, the AP will respond to the received frames, e.g.request management frames, during the MU Downlink transmission using theteachings of embodiments.

To do so, the AP builds the MU Downlink transmission with a particularRU allocation profile that takes into account the stored RU profiles ofthe uplink RUs (with AID=2045) used by STA1 and STA6. In particular, theAP provides, in the MU Downlink transmission, a first downlink RU withAID=2045 having the same allocation scheme feature (for instance sameposition) as the uplink RU used by STA1, and a second downlink RU withAID=2045 having the same allocation scheme feature as the uplink RU usedby STA6.

It means that the various resource units for the not-yet-associatedstations in both MU Downlink and Uplink transmissions, are signalledusing the same predefined association identifier not associated with anyparticular station, in particular reserved for unassociated stations,here AID=2045.

In the example of the Figure, STA1 has transmitted its probe requestframe 310 in the uplink RU at position #1 during the MU Uplinktransmission 510. In that case, the AP builds the MU Downlinktransmission with a downlink RU at position #1 which also has AID=2045.

Similarly, STA6 has transmitted its authentication request frame 340 inthe uplink RU at position #6 during the MU Uplink transmission 510. Inthat case, the AP builds the MU Downlink transmission with a downlink RUat position #6 which also has AID=2045.

Of course, another allocation scheme feature than the uplink RU positioncan be used, as introduced above.

Thanks to this approach, not-yet-associated stations STA1 and STA6 knowsthat the first and sixth resource units in the MU Downlink transmissionare destined to them, provided they are assigned to AID=2045. It meansthat, in this embodiment, two criteria are combined for thenot-yet-associated station to identify a downlink RU addressed to it:first, the downlink RU may be assigned with AID=2045; second, therelevant allocation scheme features must match with the uplink RU usedin the MU Uplink transmission when sending a previous frame, e.g. therequest management frame.

The AP 110 thus sends the responses to the not-yet-stations using thedownlink RUs 920 with AID=2045 so built (the other downlink RUs are usedconventionally). In the present example, the AP sends the probe responseframe 320 to STA1 using the first downlink RU (position #1) and sendsthe authentication response frame 350 to STA6 using the sixth downlinkRU (position #6).

Finally, the not-yet-associated stations STA1 and STA6 receive anddecode the response frames sent by the AP on these two downlink RUs inresponse to their previous request frames, and acknowledge goodreception by an uplink transmission 940.

As it is readily apparent from this Figure compared to FIG. 6 ,successive SU transmissions (630-1 and 630-2) for management frames arenow avoided, resulting in a simplification of the association procedurefor not-yet-associated STAs and a more efficient usage of the network.This is particularly advantageous to manage the association of newstations in dense networks as 802.11ax.

FIG. 10 b illustrates, using a flow chart, main steps at the AP inrelation with an MU Downlink transmission it triggers when implementingsome embodiments. These operations follow the reception of one or morerequest management frames from not-yet-associated stations, and describehow the AP transmits response frames thereto using a MU DL transmission.

At step 1050, the AP determines whether or not one or more responsemanagement frames are ready to be sent in response to request managementframes received from not-yet-associated stations during a previous MUUplink transmission.

In the affirmative, at step 1060, the AP builds a MU Downlink frame(i.e. a plurality of downlink resource units assigned to downlinktransmission from the access point within a transmission opportunitygranted to the access point) comprising, for each response frame tosend, a downlink resource unit that matches the allocation schemefeature stored for the corresponding not-yet-associated station (i.e.that matches the allocation scheme feature of uplink resource unit usedby said station to send its request frame in the MU Uplinktransmission). For instance, the downlink and uplink RUs may have thesame position in the allocation scheme used. Each such downlink resourceunit is declared in HE-SIG-B in association with AID=2045.

Next, at step 1070, the AP 110 sends each response management frame onthe corresponding downlink RU with AID=2045, to the appropriatenot-yet-associated station.

Correspondingly, FIG. 11 b illustrates, using a flow chart, main stepsat a not-yet-associated station in relation with an MU Downlinktransmission triggered by the AP according to some embodiments. Theseoperations describe how such a station decodes a response managementframe received from the AP in a MU Downlink transmission.

The not-yet-associated station has already sent a request managementframe to the AP using an uplink RU with AID=2045 in a previous MU Uplinktransmission and is waiting for a response thereof.

The process starts when a MU Downlink frame is received to determine, atstep 1150, whether or not the frame includes downlink resource unitswith AID=2045.

In the negative, the not-yet-associated station waits for a next MUDownlink frame.

In the affirmative, the station determines, at step 1160, whether or notone of the downlink RUs with AID=2045 has allocation scheme featuresmatching those stored at step 1140. This may simply consist in verifyingwhether or not a downlink RU with AID=2045 has the same position as theone (uplink RU) used in the previous MU Uplink transmission.

In case a matching downlink RU with AID=2045 is found, thenot-yet-associated station selects this downlink RU to read the framesent by the AP (step 1170). Optionally, the station may further read andcheck a MAC address specified in the frame before processing it.

The response management frame is thus decoded from this downlink RU andforwarded for instance to the MAC 802.11 layer block 804 (step 1180).

While FIG. 9 a illustrates a situation where the downlink resource unitsof the MU Downlink transmission to provide the response directly followsthe uplink resource units of the MU Uplink transmission by which therequest has been sent, within the same transmission opportunity grantedto the access point, other embodiments may provide that the uplinkresource units assigned to uplink transmission by which the request hasbeen sent and the downlink resource units assigned to downlinktransmission to provide the response are separated by one or more otherMU transmissions, either Downlink or Uplink, within the sametransmission opportunity granted to the access point.

This is illustrated in FIG. 9 b which shows that one or more MUtransmissions can be inserted between transmission 510 and transmission920.

This embodiment gives time to the AP to prepare the response managementframes.

Another situation is illustrated in FIG. 9 c where the downlink resourceunits of the MU Downlink transmission to provide the response and theuplink resource units of the MU Uplink transmission by which the requesthas been sent belong to two separate transmission opportunities grantedto the access point.

Between the two separate TXOPs, any station may contend and access tothe medium to send data.

This embodiment also gives time to the AP to prepare the responsemanagement frames.

In the embodiments of FIGS. 9 b and 9 c , the AP may avoid inserting,between the two transmissions, “intermediary” MU Downlink framescontaining a downlink resource unit with AID=2045 matching the relevantallocation scheme feature or features of an uplink RU previously used byan unassociated station to send a request frame to the AP and that isnow waiting for a response (management) frame from the AP. Thisadvantageously avoids the unassociated station to read a downlink RUwhich eventually does not contain a frame addressed to it.

It should be noted however that avoiding such “intermediary” MU Downlinkframe(s) is(are) not mandatory. If “intermediary” MU Downlink frame(s)are inserted between the two transmissions, an unassociated station thatreads a downlink RU with AID=2045 (matching its relevant allocationscheme feature or features) which contains a frame not addressed to itwill simply ignore the frame (by determining for instance whether or notthe RA field 203 is its own MAC address) and continue monitoring foranother MU Downlink frame containing a downlink resource unit withAID=2045 matching its relevant allocation scheme feature or features.

FIG. 9 d illustrates the general embodiment in which a plurality ofdownlink resource units (950) are allocated to multiple unassociatedstations within the MU DL frame. In the illustrated embodiment, severalRUs with AIDs equal to 2045 are signalled in the HE-SIG-B at locationscorresponding to UL requests. The AP may use these downlink RUs withAID=2045 to send response frames to unassociated stations, such as aprobe response and an authentication response.

Another embodiment is illustrated in FIG. 12 a in which a uniquedownlink resource unit (1210) is allocated to unassociated stations(i.e. with AID=2045) within the MU DL frame. The AP may use this singledownlink RU with AID=2045 to send a response frame to unassociatedstations as a broadcast frame (i.e. with RA field 203 set to broadcastaddress).

As explained below, as a single downlink RU with AID=2045 is provided,the unassociated stations do not check the matching with their relevantallocation scheme feature or features. They all read the frame(s) ofthis single downlink RU with AID=2045. Due to the absence of allocationscheme feature check, the position of this downlink resource unit withAID=2045 within the MU DL frame can be anywhere. FIG. 12 a illustratessteps 1058 and 1054 at the AP side of the flowchart of FIG. 10 cdescribed below.

A variation is illustrated in FIG. 12 b in which a unique downlinkresource unit (1220) is allocated to unassociated stations within the MUDL frame. This may be because the AP decides sending a unique responseto a specific unassociated station. In that case, the RA field 203 ofthe frame sent through the unique downlink resource unit with AID=2045(1220) is set to the MAC address of the destined unassociated station.FIG. 12 b illustrates steps 1053 and 1054 at the AP side of theflowchart of FIG. 10 c described below.

These illustrations show that, depending on the number of downlink RUsdefined in the MU DL transmission, the unassociated stations may switchfrom a first behaviour where they check the matching of the downlink RUswith AID=2045 with their relevant allocation scheme feature or features(e.g. if there are more than a single downlink RU with AID=2045) beforeaccessing/reading the matching downlink RU and a second behaviour wherethey do not perform the check (e.g. if there is a single downlink RUwith AID=2045) and directly access/read the downlink RU.

In the second behaviour, it is unassociated stations’ responsibilitiesto check whether the frame(s) sent over the unique downlink RU isaddressed to them or not, e.g. by checking the RA field 203 (broadcastaddress or the MAC address specific to the station). Such check of theRA field 203 may optionally be done by the unassociated stations withthe first behaviour.

Thanks to some embodiments, several RUs with AID=2045 can be used in thesame MU Downlink transmission to send response management frames torespective not-yet-associated stations. This is advantageous in denseand active networks (e.g. rail stations where a lot of stations connectand disconnect the network in a short time).

Advantageously, the AP may regularly provide a trigger frame with a lotof (possibly only) random RUs with AID=2045. Preferably the allocationscheme of the first entry of FIG. 2 f is used to offer a maximum numberof opportunities for the not-yet-associated stations to perform theirassociation procedure. The AP may thus provide, quickly after, a MUDownlink transmission matching the same allocation scheme, to providethe response management frames.

FIG. 10 c illustrates, using a flow chart, main steps at the AP inrelation with one or more MU Downlink transmissions embedding framesdestined to unassociated stations according to some other embodiments.Note that the MU Downlink transmission may also embed frames intended toalready-associated stations, but these transmissions may useconventional methods and are not further described here.

In the following description a predefined identifier value of 2045 ischosen to designate MU DL RUs reserved for unassociated stations. Ofcourse this value is given for illustration only and any otherpredefined value or signalling means may be adopted.

At step 1051, the AP determines whether there is a list of pendingframes (e.g. response management frames or any other type of frames)waiting for transmission to unassociated stations. Again, other framesintended for associated stations may also be handled in parallel orsequentially by the AP.

If the list of pending frames is not empty, it is determined at step1052 whether the list contains a broadcast frame (i.e. a MPDU packetwith a RA field 203 set to the broadcast value FF:FF:FF:FF:FF:FF). If abroadcast frame is found, it is selected at step 1053 for transmission.A single downlink RU with AID=2045 is included in a MU DL framecomprising the selected frame (step 1054). The downlink RU can belocated anywhere within the MU DL frame (an example is illustrated inFIG. 12 a ). The MU DL frame may be built at the time of inclusion ofthe downlink RU with AID=2045, or may be formed earlier by module 805 ofthe AP, for example at the time other downlink RUs destined foralready-associated stations are defined.

If the list does not contain a broadcast frame (test 1052 negative), thenumber of frames pending for transmission is determined at step 1057. Ifonly one frame is present in the list, that frame is selected (step1058) and included in the MU DL frame (step 1054). Similarly as for step1053, only one downlink RU with AID=2045 is included in the MU DL frame(as shown for instance in FIG. 12 b ).

If multiple frames are present in the list (number of frames to sendgreater than one at test 1057), multiple frames are selected from thelist at step 1059. Preferably, all response frames that follow thereception of request frames received on uplink RUs from unassociatedstations (e.g. according to flowchart of FIG. 10 a ) are selected inorder to be transmitted to the corresponding unassociated stations. Thedesign of the downlink RUs with AID=2045 for the response frames can bebased on at least one allocation scheme feature of the uplink RUs usedby the unassociated stations. Of course, the response frame for aspecific unassociated station will be sent over the downlink RU matchingthe allocation scheme feature of the uplink RU used by the same stationwhen requesting the AP.

The number of frames selected at step 1059 may be limited to a number ofdownlink RUs available, for instance of downlink RUs available to beassigned to AID=2045. This may be the case if some downlink RUs arealready assigned to specific already-associated stations.

At step 1061, multiple downlink RUs with AID value 2045 are included inthe MU DL frame. The MU DL frame is previously built or is built at thetime of the inclusion. The included downlink resource units withAID=2045 match the allocation scheme features stored for thecorresponding unassociated stations respectively (i.e. each downlink RUmatches the allocation scheme feature of the uplink resource unit usedby said station to send a frame in the MU Uplink transmission).

For instance, the AP, that received a RA RU carrying a managementrequest frame from an unassociated STA, may transmit a managementresponse frame in HE MU PPDU (i.e. MU DL frame) using a broadcast RUidentified by a STA_ID (AID) equal to 2045 and having the same RUallocation as the RU allocation of the received RA RU.

At step 1055, the MU DL frame is transmitted by the AP. Finally, at step1056, the list of pending frames is updated by removing the selectedframes that have been transmitted (and acknowledged), and the steps ofthe flowchart are repeated from step 1051.

The flowchart illustrated in FIG. 10 c describes one possibleimplementation for handling the transmission of frames for unassociatedstations according to some embodiments. However other implementationvariants may be contemplated.

For example, the broadcast frame may be given a lower priorityrelatively to other frames in the list, meaning one or more frames maybe selected first for transmission although a broadcast frame is presentin the list. The broadcast frame is then only transmitted after all or acertain number of frames (based on age or other criteria) aretransmitted from the list.

In another variant, instead of selecting multiple frames at step 1059,the AP may decide to select only one frame among the list of multipleframes to send. In this case, the MU DL frame will contain only onedownlink RU with AID=2045 comprising the selected frame. Step 1061 iscancelled in this variant. The selected frame is included in a MU DLframe as described at step 1054.

Correspondingly, FIG. 11 c illustrates, using a flow chart, main stepsat an unassociated station in relation with an MU Downlink transmissiontriggered by the AP. These operations describe how such an unassociatedstation decodes a frame received from the AP in a MU Downlinktransmission.

The process starts by checking when a MU Downlink frame (HE MU PPDU) isreceived by the station (step 1151). This is similar to step 1150 atFIG. 11 b .

If a MU Downlink frame is received (test at step 1151 positive), thestation determines at step 1152 whether multiple downlink RUs with AIDequal to 2045 are included in the received MU DL frame.

If multiple downlink RUs with an AID value 2045 are found (test at step1152 positive), the unassociated station enters a first behavior whereit checks whether a previously stored RU profile matches with the RUallocation of one of the downlink resource units having AID=2045contained in the just received MU DL frame (step 1153). A RU profile maybe previously stored by the station following the execution of flowchartof FIG. 11 a for example (e.g. transmission of a request frame in a MUUL RU with AID=2045 and storing the profile of the uplink RU asdescribed in step 1140). Thus, a RU profile is stored if theunassociated station has already sent a request frame to the AP using anuplink RU with AID=2045 in a previous MU Uplink transmission.

The matching test at step 1153 may simply consist in verifying whetheror not a downlink RU with AID=2045 has the same position as the one usedin the previous MU Uplink transmission.

The matching test at step 1153 may also be that the STA has previouslysent a management request frame in response to a Trigger framecontaining RA-RU(s) with AID set to 2045, and the broadcast RU withSTA-ID (AID) equal to 2045 has the same RU allocation as the RUallocation of the RA-RU carrying the request in the previously sent HETB PPDU.

If the test at step 1153 is positive, the unassociated station isconsidered as recipient of the matching downlink RU, which means thatthe matching downlink RU potentially contains a MAC frame destined tothe unassociated station. The matching downlink RU is then selected atstep 1154 for decoding. Optionally, the unassociated station checkswhether the RA field 203 of the MAC frame conveyed in the selectedmatching downlink RU corresponds to the unassociated station MAC addressprior to decoding.

If the test at step 1153 is negative, the unassociated station is therecipient of no downlink RU. The unassociated station waits for thereception of new MU DL frames with AID=2045 at step 1151.

At step 1155, the frame encapsulated in the selected downlink RU withAID=2045 is decoded, and forwarded for instance to the MAC 802.11 layerblock 804. The encapsulated frame may be a response frame.

If a single downlink RU with an AID value 2045 is found at step 1152(test negative), the unassociated station enters a second behavior whereit does not check any matching between a stored RU profile and thesingle downlink RU. The unassociated station is (automatically)considered as recipient of that downlink RU. The unassociated stationthen checks at step 1156 whether the RA field 203 of the MAC framecorresponds to the unassociated station MAC address or to a broadcastaddress. In the affirmative, the downlink RU is selected at step 1157and the frame contained therein decoded at step 1155. In the negative,the unassociated station waits for the reception of new MU DL frameswith AID=2045 at step 1151.

Note that in any case, and in particular when multiple downlink RUs withAID=2045 are determined at step 1152, the unassociated stationeventually decodes at most one downlink RU with AID=2045. This makes iteasy for the unassociated station to determine whether it is recipientof a downlink RU or not and, in the affirmative, to locate the downlinkRU for which the unassociated station is the recipient.

Note also that an unassociated station that receives a MU DL framecontaining RUs with the STA-ID (AID) equal to 2045, is considered as therecipient of a RU with the STA-ID equal to 2045 if one of the followingcondition occurs:

-   there is only one RU with the STA-ID equal to 2045 in the MU DL    frame (test 1152 negative);-   the STA has previously sent a (e.g. management) request frame in    response to a Trigger frame containing RA-RU(s) with AID set to    2045, and the broadcast RU with STA-ID equal to 2045 has the same RU    allocation as the RU allocation of the RA-RU carrying the request in    the previously sent MU UL frame (test 1153 positive).

According to second approaches that are based on aggregation, theinventors have contemplated using a RU in the MU Downlink transmissionfor multiple addressee stations, i.e. a resource unit intended formultiple stations (or dedicated to a plurality of stations in anequivalent wording). The access point can thus aggregate data framesaddressed to two or more stations, and transmit the aggregated dataframes over such a resource unit dedicated to a plurality of stations,from amongst a plurality of resource units forming the multi-userdownlink transmission opportunity (MU Downlink OFDMA TXOP) granted tothe access point for downlink communication to the stations. Theaggregated data frames may contain only individually addressed dataframes, i.e. data frames each with an RA addressing a single station.The aggregated data frames may contain a combination of an individuallyaddressed data frame (i.e. with RA of a single station) and a groupaddressed data frame (i.e. with RA corresponding to a multicast orbroadcast address).

Such RUs intended for groups of stations may be signaled using “groupAIDs”, contrasting with current requirements that allows only individualAIDs (i.e. associated with a single station) to be used for MU Downlinktransmission. In particular, the resource unit intended for a pluralityof stations may thus be assigned in the downlink transmissionopportunity to a predefined (group) association identifier notassociated with a specific station.

As a consequence, any station (concerned by such a group) may determine(e.g. using group AIDs) a “group” resource unit intended for a pluralityof stations, from amongst a plurality of resource units forming amulti-user downlink transmission opportunity granted to the access pointfor downlink communication to the stations, receive aggregated dataframes over the determined resource unit; and retrieve one or more dataframes addressed to the station, from amongst the received aggregateddata frames.

In fact, where any station registering with the access point beingassociated with a unique association identifier used by the access pointto assign, to the station, a resource unit in a transmission opportunitygranted to the access point, an idea proposed by the inventors consistsfor the AP to build a plurality of resource units forming a multi-userdownlink transmission opportunity granted to the access point fordownlink communication to the stations, the plurality of resource unitscomprising a “group” resource unit assigned to an association identifiernot associated with a specific station; and then transmit one or moredata frames to a station on the resource unit assigned to an associationidentifier not associated with a specific station.

So the station only determines a “group” resource unit assigned to anassociation identifier not associated with a specific station, from aplurality of resource units forming a multi-user downlink transmissionopportunity granted to the access point for downlink communication tothe stations; and thus receives one or more data frame from the accesspoint on the determined downlink “group” resource unit.

By aggregating data frames to be addressed to several stations withinthe same dedicated group RU, the proposed idea makes it possible for theAP to efficiently target a large number of stations, thereby using moreefficiently each RU (and thus reducing padding bits), avoidingduplicating the same payload over several RUs (by grouping the stationstargeted by the same multicast frame) and efficiently (i.e. at a higherbit rate) providing response management frames to the not-yet-associatedstations (thus forming a group of not-associated stations).

Also, by using AID not associated with stations during MU Downlinktransmissions, the proposed idea offers the AP with the opportunity toaddress one or more stations deprived of AID. A group RU assigned to anassociation identifier not associated with a specific station may thusbe dedicated to a plurality of stations. The stations may thus easilyidentify, in a Downlink transmission, which RU to listen to.

MU Downlink transmission is thus significantly improved compared toknown current 802.11 ax requirements.

To achieve that, the additional block 805 may act as a multiple stationRU management module for controlling usage of OFDMA resource units(sub-channels).

For instance and not exhaustively, the operations for the AP may includegenerating and sending MU Downlink frames as defined below, which MUDownlink frames identify, using specific AIDs, at least one RU intendedfor a plurality of stations instead of a single station per RU ascurrently done; and then managing the aggregation of MAC frames to beaddressed to stations of the plurality inside such resource unit.

The operations for a station different from the AP may include analyzingreceived MU Downlink frame to determine if the station is allowed toaccess an RU for itself or an RU dedicated to a plurality of stations(group RU), and in the context of such an RU dedicated to a plurality ofstations, processing the MAC frames aggregated therein to retrieve theor those MAC frames addressed to it.

However, some issues may arise regarding the acknowledgment, by thestations, of the data frames sent over the DL group RUs.

In the current 802.11ax scheme, the acknowledgment of data framesreceived over an RU is made by the addressee station to which the RU hasbeen specifically assigned. This acknowledgment is sent over a responseRU in the following MU Uplink OFDMA transmission 625 as indicated in thereceived UMRS information 264.

However, this scheme cannot operate for DL group RUs, as no specificstation is designated as the RU assignee. Furthermore, even if onestation would be so designated, it should not be allowed to acknowledgethe data frames addressed to other stations of the DL group RU.

An enhanced idea of the inventors to overcome these acknowledgmentissues relies on the signalling of different UMRS information withindifferent data frames conveyed over the DL group RU. For example if thegroup RU carries two aggregated data frames addressed to two respectivestations, respective response resource unit information is signalled toidentify a response resource unit to be used by the addressee station inthe MU Uplink OFDMA transmission 625 that follows the MU Downlink OFDMAtransmission 620 to provide a response (or acknowledgment) to dataframes to the access point.

As a consequence, an addressee station (addressed through the DL groupRU) may:

-   obtain, from data frames retrieved over the group RU, response    resource unit information identifying one response resource unit in    the MU Uplink OFDMA transmission 265, and-   then send to the access point a response (such as acknowledgment) to    the retrieved data frames over the identified response resource    unit.

Contrary to the 802.11 ax requirements limiting a single value of UMRSper RU, this enhanced idea allows the various addressee stations (viathe same group RU) to efficiently acknowledge receipt of data frames.

As the AP is able to schedule more RUs in the MU Uplink OFDMAtransmission 625 than in the MU Downlink OFDMA transmission 620, it ispossible to provide an opportunity for all the addressee stations toacknowledge their received data frames. Retransmission of data frames bythe AP is thus avoided, thereby saving channel bandwidth.

Also, this is the addressee station as specified in the RA field 210(MAC address) of the frame MAC header that can use the response RUindicated in the UMRS information specified in the HT Control field 250of the same MAC header. As a consequence, even the addressee stationswhich are not yet associated with the AP can acknowledge data frames.The association procedure can thus be simplified for the stations (usingrandom RU with AID=2045, receiving responses from the AP during MUDownlink transmission 620, and acknowledging the response duringsubsequent MU Uplink transmission 625).

To achieve that, the operations of the multiple station RU managementmodule 805 at the AP may also include the signalling, in the aggregatedMAC frames, of respective response resource unit information (e.g. UMRSvalues) identifying response resource units to be used by the addresseestations in a multi-user uplink transmission opportunity following themulti-user downlink transmission opportunity to provide their responseto the received data frames to the access point.

The operations for a station different from the AP may also includeobtaining, from the retrieved data frames, response resource unitinformation (e.g. an UMRS value) identifying one response resource unitin the multi-user uplink transmission opportunity, and sending to theaccess point a response to the retrieved data frames over the identifiedresponse resource unit.

In the description, the terms “multi-destination” RU, “multi-station”RU, “multi-STA” RU, “multicast” RU and “broadcast” RU are equivalent to“group” RU discussed above and are meant to refer to a resource unitintended for multiple stations. Note that “broadcast RU” does not meanthat the RU has to carry a broadcast data frame, but refers to theplurality of stations to which the RU is intended.

Embodiments of the aggregation-based approaches are now illustratedusing various exemplary embodiments in the context of IEEE 802.11 ax byconsidering OFDMA RUs dedicated to multiple stations.

Although proposed examples below are described with reference tomanagement frames of the 802.11 association process, their teachings arenot limited to such management frame transmission but can also beapplied to any 802.11 data frame such as those addressed to variousstations.

FIG. 13 a illustrates, using a flowchart, embodiments implemented at aphysical access point when preparing and performing a MU Downlinktransmission.

At step 1310, the AP first determines if it is willing to group severaladdressee stations for a Downlink transmission.

Three exemplary situations are proposed here.

In the case of station association procedure, stations may send requestmanagement frames to the access point within procedures of associating(i.e. registering) the station with the access point. In other words,the access point may receive request management frames (310, 340, 360)from stations willing to associate (i.e. register) with the accesspoint, and intends to answer to those stations by grouping together theresponse management frames (320, 350, 370) in the same group RU intendedfor a plurality of addressee stations.

The request management frames may have been received either or both viaprevious Single User communications or via a previous Trigger Frameemitted by the AP (typically the TF 530 as regards to the FIG. 6 ), suchtrigger frame allocating some random RUs with an AID equal to 2045 valuein order that some request management frames are sent bynot-yet-associated stations in corresponding RU or RUs during the Uplinktransmission phase 510.

Also, the AP may group stations with regards to a common interest toreceive data frames. For instance, the access point receives a multicastframe (e.g. from an upper OSI layer) to be addressed to a plurality ofaddressee stations, and may thus consider forwarding the multicast frameto the addressee stations using a group RU dedicated to this pluralityof stations.

Another example is the case where the access point determines there aresmall data frames to be transmitted to stations, given a size of thedownlink transmission opportunity and a size threshold (and possibly thesize of RUs), that could be grouped into a single RU to reduce paddingbits. More generally, the AP may consider using a special group toconvey any MAC frame (to be transmitted) which does not belong to anexisting individual transmission of the MU Download transmission. The APmay for instance seek to use the individual RUs to convey the largestMAC frames, in order to fill an “MPDU collector” RU or “collecting RU”(thus a group RU) with the maximum of remaining MAC frames (that aresmaller).

As example, the collecting RU may collect any pending MAC frame storedin an EDCA buffer of the AP, and for which an assignment of anindividual RU is not efficient (too much padding needed - for instanceSTA3 and STA8 in FIG. 6 ).

Once the AP has determined one or more groups of addressee stations withthe corresponding MAC frames to be transmitted, an RU (thus named groupRU, broadcast RU, multicast RU or multi-station RU) is assigned to eachgroup so determined, at step 1320.

For instance, a group RU may be allocated to convey the responsemanagement frames (320, 350 or 370) in response to requests previouslyreceived from not-yet-associated stations.

In a preferred embodiment, the AID value assigned to this group RU formultiple stations takes the predefined value 2045 (known by all 802.11axnodes compliant with the present idea). One may note that this value isthe same value as the one used to indicate the RU dedicated or assignedto not-yet-associated stations in the MU Uplink transmission (510 inFIG. 6 ), to speed up their association procedure.

As a consequence, if a request management frame is sent (by a station)in a prior resource unit forming part of an uplink transmissionopportunity granted to the access point for multi-user uplinkcommunication from the stations, the prior resource unit being assignedto stations not yet associated with the access point, the group resourceunit assigned at step 1320 and the prior resource unit used aresignalled in the downlink and uplink transmission opportunitiesrespectively, using the same prefixed association identifier (notprovided to a specific station by the AP), here AID=2045.

One may note that, even without aggregating MAC frames in the RUdedicated to not-yet-associated stations, the sole idea of providing anRU with an AID reserved for not-yet-associated stations for Downlinktransmission improves (speeds up) the association procedure for suchstations. Such RU may be used for a single not-yet-associated station.

A group RU may also be assigned to convey the multicast frame intendedto several addressee stations. A predefined AID may be used in thisrespect, for instance AID=2042 known by all the 802.11ax nodes compliantwith the present idea.

Also, the collecting RU to collect small pending MAC frames may besignaled using AID=0.

Other variants may be proposed. For instance, in the context of multipleBSSs (“virtual APs”) managed by a single physical AP, the AP may assigna unique AID value to respectively each of the BSSs it manages, meaningeach BSS has a unique AID value not associated with a specific station(but with the whole BSS). For instance, the AID value may be the indexof each BSS : if ‘n’ is the maximum number of virtual APs managed by thephysical AP (as example, this value is specified in the MaxBSSIDIndicator in the Multiple BSSID element of beacon and probe responseframes), then AIDs 1 to n are assigned to respectively BSSs 1 to n.

Each non-representative AP can use only its own AID. However, therepresentative AP can use any AID of the VAPs.

In this context, the representative AP may provide, in a MU Downlinktransmission, one or more collecting RUs specific to one or morerespective BSSs, by using the respective AIDs. The AP may thus selectthe AID of the BSS for which it is about to transmit frames.

Also, the representative AP may signal random RUs in a TF (MU Uplinktransmission) assigned respectively and individually to specific BSSs:first random RUs are assigned to AID=i to restrict the access tonot-yet-associated stations willing to register with VAP i, while secondrandom RUs are assigned to AID=j to restrict the access tonot-yet-associated stations willing to register with VAP j. RUs havingthe same AIDs can be used in the MU Downlink transmission to transmitthe response management frames related to each BSS.

Once the one or more group RUs dedicated to groups of stations have beendetermined, step 1330 consists for the AP in concatenating oraggregating, for each group RU, all the pending MPDU frames for thecorresponding group of stations. For the following, the term “Dataframes” in further illustration of steps 1330 and 1340 is wellunderstood to correspond to any frame pending in the outbound MACtransmission queue (that is to say including, without restriction, anyData frame coming from application layer 801 and any 802.11 managementframe useful for the MAC layer 804 like those of 802.11 associationprocedure).

For the management frames, all the response MAC management framesprepared by the AP for the not-yet-associated stations can be aggregatedtogether into an HE-MU PPDU (up to the size of the PPDU given thereserved TXOP).

For the multicast frame, responsive to the multicast frame reception,the access point may generate a plurality of data frames includingpayload of the multicast frame, to be each individually addressed to arespective one of the addressee stations. The AP thus aggregates thegenerated data frames including payload of the multicast frame (up tothe size of the PPDU given the reserved TXOP). Of course, if the TXOPdoes not provide enough space to transmit all the generated data frames,the remainder may be transmitted during one or more next MU Downlinktransmissions.

Also, the AP may aggregate together (and up to the size of the PPDUgiven the reserved TXOP) the MAC frames stored in its EDCA buffers forstations that have not yet been addressed by other RUs of the same MUDownlink transmission. Given this constraint, the aggregation for thecollecting RU is processed at the end (as the last RU).

The AP may follow the principle of 802.11 ax A-MPDU aggregation forclassical RU, but slightly modify it to allow MPDUs of the same A-MPDUto be addressed to different stations. In other words, aggregation rulesare slightly modified for a group RU (“broadcast RU” according to the802.11 ax standard terminology) in order to support addressing severalstations inside a single A-MPDU. This does not mandate any modificationof the 802.11 baseline, as this mechanism is only limited to 802.11 axstations of the invention involved in the restricted context of groupRU.

For example, when transmitted by a 802.11 ax AP in a RU intended formultiple STAs (e.g. Broadcast RU), the MPDUs within an A-MPDU may havedifferent RAs. The RA may be the MAC address of one of the multiple STAsor a broadcast MAC address. Address type (individually addressed orgroup addressed) and address values of MPDUs may be different inside anA-MPDU in an RU intended for multiple STAs.

Any other aggregation mechanism (MAC Service Data Unit (MSDU)aggregation, MAC Protocol Data Unit (MPDU) aggregation, concatenation ofA-MPDU frames, or any combination of those schemes) can be used toconcatenate MAC frames for various stations.

To make it possible for the stations to efficiently retrieve their ownMAC frames, the access point sets, in each data frame to be aggregated,a MAC address field 210 to a MAC address of the addressee station.

If the MAC address field contains a broadcast address, the MAC frame maybe retrieved by all stations that belong to the group RU. Note that theMAC frame with a broadcast address may be retrieved by all stations ofthe BSS if the group RU is dedicated to a group to which all stations ofthe BSS belong to, or a group defined to be accessible to all stationsof the BSS.

If the MAC address field contains a multicast address (i.e. defining amulticast group of stations), the MAC frame may be retrieved by allstations that belong to both the group RU and the multicast group.

Next at step 1340, the MU Downlink PPDU formed of each RU is sent by theAP on the corresponding RU of the communication channel.

Regarding the groups of stations, it means that the aggregated responsemanagement frames are transmitted on the group RU with AID=2045 or oneach group RU with AID=i for the response management frames related toBSS i (in case of multi-BSSs); the aggregated generated frames includingthe payload data of the multicast frame are transmitted over the groupRU with AID=2042 as example; and the aggregated collected frames aretransmitted over the last RU of the channel, the group RU with AID=0(possibly with AID=j for collected frames related to specific BSS i incase of multi-BSSs).

The other RUs (assigned to individual stations) are handledconventionally.

To ensure efficient processing by the stations, the downlinktransmission opportunity may include an ordered signalling (in theHE-SIG-B preamble of 802.11 ax MU DL frame) of assignments of resourceunits of the plurality to one or more stations, the ordered signallingfirst defining each assignment of a resource unit to an individualstation (RU with an AID associated with a single station), next definingeach assignment of a resource unit to a group of stations (AID=2042 or2045 or i in case of multi-BSSs, in the examples above), then definingan assignment of the collecting resource unit (AID=0) to any station notyet associated with a resource unit. This advantageously allows astation to disregard any further RU analysis in the same HE MU PPDU onceit has found one RU (individual or group) addressed to it.

One may note that the aggregation-based approach advantageously keepsthe strict usage of a unique AID presence in the RU Allocation of theHE-SIG-B preamble, despite the use of groups of stations or thetransmission to (not-yet-associated) stations having no AID.

The Downlink transmission opportunity thus includes resource units thatthe stations may read using a conventional 802.11 ax scheme (e.g. byidentifying the RU linked with their AID) or by using the newly proposedscheme (e.g. by identifying a RU linked to a group AID) as now describedwith reference to FIG. 13 b .

FIG. 13 b illustrates, using a flowchart, embodiments implemented at anon-AP station to handle group RUs dedicated to groups of stations in MUDownlink transmissions from the AP.

The non-AP station can be any station already associated with the APemitting the MU Downlink PPDUs, or any not-yet-associated station whichis in the process of associating with the AP emitting the MU DownlinkPPDUs.

At step 1350, a MU Downlink frame made of per-RU PPDUs is received fromthe physical access point, and the station determines which RU isaddressed to it. RUs assigned to individual stations are processedconventionally.

Specific processing is required for the situation where the station isinvolved in a group RU conveying data for a group of stations. In thatcase, the station determines such a group resource unit dedicated to aplurality of stations, from amongst a plurality of resource unitsforming the downlink transmission opportunity granted to the accesspoint for downlink communication to the station.

For a not-yet-associated station, it means determining a group resourceunit assigned to stations not yet associated with the access point. Thisis to retrieve a response management frame from the access point to thesent request management frame. This may be simply performed by searchingin the HE-SIG-B preamble of the received MU Downlink frame for an RUwith an AID equal to 2045 or an RU with an AID equal the BSSID (in caseof multi-BSSs).

If no group RU is found, the process ends and the not-yet-associatedstation sets its NAV (duration is obtained from L-SIG field of thereceived frame).

If such group RU with AID=2045 is found, next step is step 1360.

Optionally, the not-yet-associated station may analyze the received MUDownlink frame, and thus determine a resource unit assigned to stationsnot yet associated, only if a request management frame sent by thestation is pending (i.e. no response has been received from the AP).This request may have been previously transmitted during a prior MUUplink transmission (for instance during 510). In particular, anunassociated STA may disregard any RU with a STA-ID set to 2045 in a HEMU PPDU received from a HE AP for which this STA is not in apre-association context (which means that the unassociated STA has notsent any association request to that AP).

For an already-associated station, the operations may be different. Thestation may first scan through resource units assigned to individualstations to verify whether a resource unit in the received MU Downlinkframe is individually assigned to the station or not, and in case ofnegative verification only, the station determines a group resource unitdedicated to a plurality of stations from the not-yet scanned resourceunits of the plurality.

Such processing order derives from the order of declaring the RUs in theMU Downlink frame as indicated above with reference to FIG. 13 a : theindividual RUs are first declared, followed by the group RUs (AID=2042for instance for multicast), followed by the collecting group RU(AID=0). In this situation, if the station detects a single RU addressedto it, the process of FIG. 13 b ends and the station analyzes thecorresponding RU in a conventional 802.11 ax way. Otherwise, the stationsearches between the group RUs if one of them is addressed to it. Thismay be performed using bit masking on the AID (for instance if group AIDhave the same most significant bits) and/or by detecting predefinedAIDs. Thus, the station scans through group resource units assigned tolists (groups) of stations to verify whether the station belongs to alist associated with one of the scanned group resource units.

This makes it possible for the station to stop analyzing the MU Downlinkframe as soon as a group RU dedicated to a group to which the stationbelongs it is detected. For instance, if the station knows it isinvolved in a multicast communication (e.g. due to exchange at anapplication layer - see module 801), the station may scrutinize anygroup RU dedicated to multicast (AID=2042 in the example here).

In case of positive verification (the station belongs to a list), thedetermined group resource unit to retrieve the data frames is the oneassigned to the list that includes the station (e.g. with AID=2042).

On the other hand, in case of negative verification only, the determinedgroup resource unit is the collecting resource unit (AID=0) used toconvey data frames for any station not assigned, individually or througha list, to another resource unit forming the downlink transmissionopportunity. The station will thus monitor the collecting RU.

Of course, any other order for considering the RUs may be implemented,so that the station may decide to stop its analysis upon either thedetection of a single RU addressed to it or a group RU dedicated to agroup to which the station belongs.

Finally, if a group RU is found (AID=2042, 2045 or 0 in the aboveexamples), step 1360 is executed where the station reads the determinedgroup RU and thus receives aggregated data frames from the AP. All theMPDUs forming the A-MPDU received on the determined group RU areprovided to the MAC layer (process 805) for further analysis.

At step 1370, the station compares a MAC address of each aggregated dataframe (the RA field 210 of each MPDU forming the A-MPDU) with its ownMAC address. This is to retrieve one or more data frames, if any,addressed to the station, from amongst the received aggregated dataframes. The STA may thus retrieve one or more frames, carried in a RUintended for multiple STAs, that are addressed to this STA based on theRA field of each MPDU frame.

Symmetrically to what has been made at the AP, the principle of 802.11ax A-MPDU disaggregation for classical RU is slightly modified at thestation to analyze the MAC address of each MPDU. This is to avoidstopping the de-aggregation process as soon as one MPDU not matching thereceiver station address is found, as done with legacy A-MPDUprocessing. In other words, aggregation/de-aggregation rules areslightly modified for a group RU (“broadcast RU” according to the802.11ax standard terminology) in order to support addressing severalstations inside a single A-MPDU. This does not mandate any modificationof the 802.11 baseline, as this mechanism is only limited to 802.11 axstations of the invention involved in the restricted context of groupRU.

The station then keeps only the MPDU or MPDUs having a MAC address 210equal to the station’s MAC address, a multicast MAC address of a groupthe station belongs to, or a broadcast MAC address. In other words,unassociated stations (e.g. which have sent requests to that AP) willdecode that group RU (or broadcast RU according to the 802.11 axstandard terminology), then de-aggregate and filter associationmanagement response frames according to RA MAC addresses.

Next, at step 1380, all extracted MPDUs addressed to the stations areforwarded to upper layer stacks (for instance to the application layer801).

The station may not acknowledge receipt of the retrieved data frames, tothe access point (no additional step is shown in the Figure). Thus, allMU Downlink MPDU transmitted in the RU dedicated to a group of stationscontain a No-Ack indication.

In some cases, it would be worth having an acknowledgment of the dataframes sent over the group RU. However the conventional 802.11axmechanisms allow a single station per RU (thus also per group RU) toacknowledge receipt of data. This cannot meet the requirements ofmultiple acknowledgments for group RUs. Thus, an acknowledgment policymay be implemented in which the station sends an acknowledgment of theretrieved data frames only if the retrieved data frames include the lastreceived aggregated data frame. It means that only the last MPDU in theA-MPDU is explicitly acknowledged by its addressee station (according to802.11ax standard, in an RU of MU ACK following the MU Downlink frame inthe same TXOP). As a consequence, the other MPDUs may be implicitlyacknowledged by the acknowledgment of the last MPDU. This may be anincorrect acknowledgment as some stations may not have actually receivedtheir data frames from the AP.

In the specific case of not-yet-associated stations receiving a responsefrom the AP, an acknowledgment of the retrieved response may be sent bythe receiving station, in a next resource unit forming part of a nextuplink transmission opportunity granted to the access point for uplinkcommunication from the stations, the next resource unit being assignedto stations not yet associated with the access point (i.e. a next randomRU with AID=2045 in an MU Uplink TXOP). This acknowledgment scheme isalso not really efficient as the not-yet-associated stations may notactually access a random RU in a short delay. As a consequence, the APis not aware of the correct reception of the data frames and mayschedule their retransmission, thereby wasting channel bandwidth.

To improve network efficiency, this acknowledgment may further beaggregated in this next RU (with AID=2045 for instance) with any furtherrequest management frame. For instance, if a probe response frame 320 isreceived in the MU Downlink frame according to the approach, then thestation may provide the acknowledgement 330 corresponding to 320together with the next request management frame (here authenticationrequest frame 340), in an RU with AID=2045 in the next MU Uplinktransmission 510. This is to make the association procedure progressingfaster for the station. Again, it may require a lot of time (because ofcontention) before the not-yet-associated stations access the mediumwith a new random RU.

FIG. 14 illustrates the benefits of using group RUs with reference tothe exemplary situation of FIG. 6 described above.

TXOP#1 is the same as in FIG. 6 with not-yet-associated stations STA1and STA6 sending request management frames to the AP in the RU withAID=2045.

As readily apparent from the HE-SIG-B preamble of MU Downlink frame1420, group AIDs are used, in particular AID=0 (for collecting smallframes), 2042 (for multicast) and 2045 (for not-yet-associatedstations). As indicated above, the HE-SIG-B preamble may declare firstthe RUs for individual stations (here 2 and 7), followed by the groupRUs (here 2042 and 2045), followed by the group collecting RU (here 0)which is dedicated to “all other” associated stations.

The group RU with AID=2045 is used to convey concatenated MPDU framesaddressed to one or multiple not-yet-associated stations, here a proberesponse frame intended to STA1 and an response authentication frameintended to STA6. In other words, a single RU with AID=2045 inside a802.11ax Multi-User frame (HE MU PPDU) concatenates associationresponses to several unassociated STAs. As a consequence, successive SUtransmissions (630-1 and 630-2 in FIG. 6 ) for management frames areavoided, resulting in a simplification of the association procedure fornot-yet-associated STAs and a more efficient usage of the network. Thisis particularly advantageous to manage the association of new stationsin dense networks as 802.11ax.

The group RU with AID=2042 is used to convey concatenated MPDU framesaddressed to stations belonging to a multicast group, here stations STA5and STA4. A single 802.11 A-MPDU frame is used and conveyed inside asingle RU. This avoids RU duplication compared to conventional 802.11axscheme.

The group RU with AID=0 is used to convey concatenated MPDU framesdedicated to a plurality of associated stations, for instance small MPDUframes which individually would not efficiently fill an entire RU (evenif of smallest band, e.g. 26 tones) or when the limitation of number ofRUs (maximum 9 per 20 Mhz band) is already reached. Such concatenationallows limiting padding in the RUs and thus reduces latency of smallframes compared to conventional 802.11ax scheme.

As shown in the Figure, the MU Downlink transmission 1420 is followed byan MU ACK period 1440 belonging to the same TXOP#2. For instance, anacknowledgment frame 1440 according to the 802.11ax standard may beused, in which no acknowledgment is provided for group AIDs or anacknowledgment is provided by the station to which the last transmittedMPDU is addressed).

In some embodiments, the MU Downlink frame 1420 is followed byindividual immediate acknowledgment frames according to FIG. 15described below.

In these embodiments, each of the stations addressed through a group RU(during MU Downlink transmission 1420) obtains, from its retrieved dataframes, an individual UMRS Control field 264 identifying which responseresource unit (1440-A/B/C/D) to be used during the MU Uplinktransmission 1440, and then sends to the access point the acknowledgmentframe over the identified response resource unit.

This requires for the AP to signal, in two (or more) aggregated dataframes addressed to two respective stations, a respective UMRS Controlfield identifying a response resource unit to be used by the addresseestation in the MU Uplink transmission 1440 following MU Downlinktransmission 1420 to provide a response to data frames to the accesspoint.

Thanks to this approach, different UMRS Control fields are conveyedwithin (aggregated) MPDUs over the same DL group RU.

FIG. 16 a illustrates, using a flowchart, an improvement of the processof FIG. 13 a (at the access point) to provide efficiently frameacknowledgment in case of group RUs. The same step references as FIG. 13a are used when unmodified.

Thus, as described above, initially the AP determines one or more groupsof addressee stations with the corresponding MAC frames to betransmitted (step 1310), and a group RU of the MU Downlink transmission1420 is assigned to each determined group of stations (step 1320).

As already disclosed, a group RU may be used to convey the associationrequest/response frames intended to at least one non-associated stations(group RU with AID=2045), or to convey the multicast frame intended toseveral addressee stations (group RU with AID=2042), or any packetcollection for several stations (group collector RU with AID=0).

In embodiments, the AP may consider the total number of stations to beaddressed in the MU Downlink transmission 1420 (through individual RUsand group RUs) when selecting the groups. In particular, this totalnumber may be less or equal to the maximum number of response RUs thatthe AP may define in the MU Uplink transmission 1440 for acknowledgment.Preferably, the AP only takes into account the stations that will haveto (that is to say, are solicited to) acknowledge receipt of the dataframes. This is to provide a response or ack RU for each station.

Once a group has been selected, the MAC frames to be transmitted for thegroup are gathered (step 1330 a).

Next, the AP has to signal using UMRS Control fields 264 which responseRU each station of the group has to use to acknowledge its data frames.This is made through steps 1610 and 1611 to signal, in two (or more)aggregated data frames addressed to two respective stations, arespective UMRS Control field identifying a response resource unit to beused by the addressee station in the MU Uplink transmission 1440following MU Downlink transmission 1420 to provide a response to dataframes to the access point.

First, the AP determines at step 1610 the number of scheduled RUsrequired for the next MU Uplink communication 1440 based on the numberof stations addressed by the frames conveyed in the group RU and theother RUs of MU Downlink transmission 1420.

The number of response RUs for the current group in MU Uplinkcommunication 1440 equals at most the number of stations of the group.

This complies with the requirement that a given addressee station hasonly one response RU to use for its next MU Uplink transmission.

This also allows a given addressee station not to be assigned a responseRU in case of no response (acknowledgment) is expected by the AP. As aconsequence, the AP may only take into account the addressee stationsthat have to provide a response or acknowledgment: i.e. the stationssupporting the UMRS signalling (i.e. if the station has set the UMRSSupport subfield to 1 in the HE MAC Capabilities Information field ofthe HE Capabilities element it has exchanged with the AP during itsassociation procedure, usually within the probe request frame) and forwhich the AP expects a response or acknowledgment. This approach reducesthe amount of response RUs necessary. Furthermore, as the number ofresponse RUs is limited, it may help increasing the number of addresseestations for the MU Downlink transmission 1420.

As the number of relevant addressee stations (that have to respond) mayvary, the configuration by AP of the next MU Uplink transmission 1440 interms of response RUs is directly impacted: the AP may have to provide amore or less large number of response RUs (one response RU for each DLindividual RU, several response RUs for a DL group RU).

Thus, the access point may configure the MU Uplink transmission 1440 insuch a way it includes a number of response resource units based on anumber of stations addressed in the MU Downlink transmission 1420. Inparticular, this number of response RUs may be at least, but also thesame as, a number of stations that have to provide a response to dataframes addressed to them over any resource unit of the MU Downlinktransmission 1420.

Also the AP may design the MU Uplink transmission 1440 so that therequired response RUs encompass the whole 20 MHz channel.

FIG. 15 shows an example of variation in the RU configuration between MUDownlink transmission 1420 and MU Uplink transmission 1440. Some DL RUsare wider than the next UL response RUs.

For instance, 802.11ax supports a maximum number of nine RUs per 20 MHzchannel: an elementary RU is thus 26-tone width. As a consequence therecannot be more than nine 26-tone response RUs per 20 MHz channel of theMU Uplink transmission 1440. If a group RU is addressing two stations(with acknowledgment support for all stations), then the maximum numberof DL RUs is reduced by one (that is to say only eight RUs in MUDownlink direction, which then triggers nine response RUs in MU Uplinkdirection). As a result, one of the eight DL RU can be widened to fulfilthe 20 MHz band.

This consideration has less or no impact for the sake of the presentembodiments, because the group RU is intended to address severaladdressee stations and embeds more data frames than a conventionalindividual RU. In other words, making a group RU wider than anindividual RU is somewhere useful.

In some embodiments, the AP may decide not to use one or more DL RU inMU Downlink direction (for instance to avoid widening some RUs to coverthe full band). Unused RUs in MU Downlink transmission 1420 may beindicated using a specific AID in the HE-SIG-B PHY header, for instance2046. Based on this AID, the stations can avoid considering such RUs.This usage may be useful for the AP to avoid emitting padding, and thussaves its power consumption. As a result, the AP may schedule one usedgroup RU and unused RU(s) in DL transmission such as to encompass thewhole frequency band (e.g. 40 MHz) of the response RUs specified withregards to the group RU.

Next, once the AP has determined a set of available response RUs for thecurrent group, it signals such response RUs to the stations concernedusing UMRS Control fields 264. This is step 1611. The assignment of theavailable response RUs to the stations of the group may be made usingany assignment scheme (random, according to AID order and RU order,etc.).

In this step, for each addressee station of the group from which aresponse is desired, the UMRS Control field set with the correspondingassigned response RU is inserted in the HE MAC header of at least onedata frame addressed to this station (i.e. one MPDU having its RA field210 set to the MAC address of the addressee station). When two or moreindividually addressed MPDU frames are received over a group RU, theUMRS Control fields within MPDUs carried in the A-MPDU have the samevalue per given addressee station. That is to say, if several framesaddressed to a same STA (identified by RA field set to the STA MACaddress) have a UMRS Control field, they all have the same UMRS Controlfield value.

Thus, in two data frames addressed to two respective stations of thegroup, there is inserted two respective response resource unitinformation items identifying respective response RUs to be used by eachaddressee station in MU Uplink transmission 1440 following MU Downlinktransmission 1420. This is for the stations to provide aresponse/acknowledgment to data frames to the access point.

Once the UMRS information items have been inserted in various dataframes intended for the stations of the group, step 1330 b consists forthe AP in concatenating or aggregating all the pending MPDU framesselected at step 1330 a into a single A-MPDU to be sent over a group RUduring MU Downlink transmission 1420. This is for example the case forgroup RU with AID=0 in FIG. 15 .

Due to above-mentioned constraints on the number of addressee stationsduring MU Downlink transmission 1420 and the number of response RUs,step 1330 b may thus aggregate data frames to be addressed to a numberof stations in such a way a total number of stations addressed over theplurality of resource units forming MU Downlink transmission 1420 doesnot exceed a determined maximum number of stations, such maximum numberdepending on or being a maximum number of elementary (26-tone) resourceunits that can be defined within MU Uplink transmission 1440.

Next, step 1340 ensures the A-MPDU to be transmitted over the allocatedgroup RU.

FIG. 16 b illustrates, using a flowchart, an improvement of the processof FIG. 13 b (at a station) to perform efficient and immediate frameacknowledgment in case of group RUs. The same step references as FIG. 13b are used when unmodified.

After the station has determined (step 1350) a group resource unitdedicated to a plurality of stations, from amongst a plurality ofresource units forming MU Downlink transmission 1420 granted to theaccess point for downlink communication to the stations, has received(1360) aggregated data frames over the determined group resource unit,and has retrieved (1370) one or more data frames addressed to it, fromamongst the received aggregated data frames, the station processes thepayload of the retrieved data frames, for instance by forwarding them toupper layer stacks (step 1380).

Next the station has to respond to the received data frames. This may bea sole acknowledgment or response data as provided by the upper layerstacks as the outcome of the payload processing. The responding processis made through steps 1620-1622.

In step 1620, the station retrieving personal data frames over the groupRU during MU Downlink transmission 1420 obtains an UMRS Control field264 from the MAC header of at least one of the retrieved data frames.

Thanks to this information, the station now knows which response RU tobe used in the next MU Uplink transmission opportunity 1440.

Note that the station may read only the first UMRS Control fields foundwithin the received and retrieved data frames intended for it. However,in some embodiments, in particular when the various data frame mayinclude data from different traffic classes or queues, the station mayconsider all the retrieved data frames to determine for which type oftraffic data the station has to provide a response or acknowledgment. Inthis configuration, the station may thus build a multi-TIDacknowledgment.

Once the response RU is known from the UMRS information, the station maywait for a SIFS (step 1621). This is implemented when an immediateacknowledgement is required.

Next, the station transmits its response or acknowledgment over theresponse RU identified at step 1620. This is step 1622.

As a consequence, the AP receives, over the various response RUs of MUUplink transmission 1440, various acknowledgment from the stationsaddressed during MU Downlink transmission 1420, including thoseaddressed over individual RUs and those addressed over group RUs.

One can note that this acknowledgment scheme is extremely suitable fornon-yet-associated stations. In details, the UMRS Control field 264 doesnot require any AID because each addressee station knows thisinformation retrieved from a personal data frame is targeted to it only.This is fully suitable for the non-yet-associated stations that have notyet assigned AIDs. The proposed approach thus advantageously takesadvantage of the UMRS format which does not require any AID, with a viewof supporting acknowledgment of association frames exchanged via MUcommunications.

Back to FIG. 15 , some benefits of the proposed acknowledgment in caseof group RUs are explained.

Conventional acknowledgment through UMRS signalling makes it possiblefor the stations STA2, STA7 and STAn receiving data frames over DLindividual RUs to send their acknowledgment over respective responseRUs. The link between UMRS signalling and the response RUs is shownusing plain arrows.

Thanks to the aggregation-based approach, two or more stations addressedthrough the same group RU are provided with respective UMRS Controlfields in order for them to find their response RUs.

In the proposed example, STA3 and STA8 are addressed through group RUhaving AID=0. One MPDU addressed to STA3 has an UMRS Control field 264identifying UL RU 1440-A, and one subsequent MPDU addressed to STA8 hasits UMRS Control field 264 indicating UL RU 1440-B. The link betweenUMRS signalling and the response RUs is shown here using dotted arrows.

As shown, the group RU with AID=0 can be larger (e.g. 56-tone RU) incomparison to the two UL response RUs 1440-A and 1440-B (e.g. 26-toneeach).

The same situation appears for group RU with AID=2045 which conveys APresponse data frames to not-yet-associated stations. As shown by thedotted arrows, the AP response data frames trigger two UL response RU1440-C and 1440-D. In the figure, the AP has decided to allocate thesetwo UL response RUs as non-contiguous. In addition, they do notnecessarily overlap the same frequency band as the DL group RU.

In fact, the assignment of the response RUs may be totally decorrelatedfrom the assignment of the DL individual or group RUs. One constraint isthat the response RUs be within the same composite channel (as indicatedin the HE-SIG-A field: 20 MHz, 40 MHz, 80 MHz) for MU Downlink OFDMAtransmission as the DL individual or group RUs, but not necessarilywithin the same 20 MHz channel.

Yet another example regards group RU with AID=2042 to transmit amulticast data frame to STA4 and STA5. The AP may decide to not includean UMRS Control field in the data frame, as the latter is multicast andthus does not require to be acknowledged.

Embodiments of the present invention may be implemented in all 802.11 axcompliant AP and non-AP stations. Alternatively, 802.11 ax compliant APand non-AP stations may optionally implement features of embodiments ofthe present invention. For this purpose, supported features may bedeclared by a station and/or an AP and execution of flowcharts accordingto embodiments of the invention may be adapted or made conditional tothe supported features.

For example, supported features may be declared by means of managementframes exchanged during the discovering phase (cf. FIG. 3 ). Forinstance, amongst the 802.11 capabilities exchanged between the AP and astation through the probe request frame 310 (or beacon) and the proberesponse frame 320, one or more capability bits are added for signalingwhether or not a feature, a set of features or an embodiment is/aresupported by a 802.11 ax device. Request management frames may have beenreceived by any previous MU or SU communications.

In an implementation, allowing aggregated MPDUs in a same A-MPDU to beaddressed to different stations is considered as an optional feature. Itis thus subject to the implementation of an 802.11 ax compliant deviceto have this feature supported or not. Still, the device has to declarethe status of its capabilities, for example during discovering phase.For the feature discussed in this implementation, one capability bit isadded. This informs the HE AP of which STAs to consider in the multi-STAA-MPDU aggregation scheme. The capability bit is referred to as“Multi-STA Aggregation In Broadcast RU Support”. Alternate naming mayalso be used for this capability bit such as “Multi-STA Aggregation InGroup RU Support”, “Multi-STA Aggregation Support”, or MSAS capabilitybit for short.

FIG. 17 shows an example format of an HE Capabilities element 1700exchanged between a station and an AP and including the capability bitaccording to one implementation variant of the invention.

According to 802.11ax, a 802.11ax compliant station (also referred to asHigh Efficiency station, or simply as HE STA) declares that it is an HESTA by transmitting the HE Capabilities element. The HE Capabilitieselement contains a number of fields that are used to advertise the HEcapabilities of an HE STA that are not all detailed here. Among thefields there is a HE MAC Capabilities Information field 1710 thatcontains a number of subfields and reserved bits.

A capability bit is added in the HE MAC Capabilities Information fieldaccording to an implementation variant. Proposal is thus to add the“Multi-STA Aggregation In Broadcast RU Support” capability bit in asubfield 1721 of the HE MAC Capabilities Information field 1710. Thesubfield 1721 may use for example bit position B42 declared as reservedin 802.1 1ax standard Draft v. 2.2. It is of course understood that anyother position for the subfield 1721 may be considered, either withinthe HE MAC Capabilities Information field 1710, or within other fieldsof the HE Capabilities element 1700.

The “Multi-STA Aggregation In Broadcast RU Support » (MSAS) subfield mayhave different interpretations depending on whether the subfield is setby the AP or a non-AP station.

In case the capabilities are those declared by the AP:

-   If the MSAS capability subfield is set to 1, the AP (identified by    the BSSID value used in the management response frame or beacon    frame that conveys the capabilities) supports the capability to    generate an A-MPDU that contains frames addressed to several    (distinct) stations when the A-MPDU is directed to be transmitted in    a downlink RU intended to several stations (group RU); and-   If the MSAS capability subfield is set to 0, the AP does not support    the capability to aggregates within an A-MPDU frames addressed to    multiple stations (unless broadcast MAC MPDUs are aggregated).

In case the capabilities are those declared by a station:

-   If MSAS capability subfield is set to 1, the station supports the    receiving of an A-MPDU that contains frames addressed to several    stations in a downlink RU intended to several stations (group RU);    and-   If MSAS capability subfield is set to 0, the station does not    support the capability to receive a MPDU addressed to it within an    A-MPDU containing frames addressed to multiple stations (unless    broadcast MAC MPDUs are aggregated).

Table below summarizes the definition and the encoding of the subfieldMSAS 1721.

Subfield Definition Encoding Multi-STA Aggregation In Broadcast RUSupport For an AP, indicates support for generating an A-MPDU thatcontains frames addressed to several stations, in a DL Broadcast RU. Fora non-AP STA, indicates support for receiving an A-MPDU that containsframes addressed to several stations, in a DL Broadcast RU. Set to 1 ifthe STA supports the Multi-STA aggregation functionality in a DLBroadcast RU. Set to 0 otherwise.

FIG. 18 a illustrates, using a flowchart, steps performed by an AP whentransmitting data to stations.

Steps 1801 and 1802 concern, respectively, advertising the capabilitiesof the AP to the stations and receiving the advertised capabilities fromstations. These steps can be executed in any order and may be performedat an early stage such as the discovering phase as discussed above.

At step 1803, the AP builds an A-MPDU of one or more MAC frames fortransmission in a group RU. Here the building of the A-MPDU depends onthe capabilities of the AP and/or the capabilities of the addresseestations of the MAC frames to be sent. This means that certain rulesneed to be followed by the AP for the building of the A-MPDU.

If the AP supports generating an A-MPDU that contains frames addressedto several stations, the Address type (individually addressed or groupaddressed) and address values of MPDUs may be different inside an A-MPDUin an RU intended for multiple STAs. In such a case, for constructing anA-MPDU with MPDU frames addressed to several receivers and carried inbroadcast RU of an HE MU PPDU, the HE AP shall only consider thosereceiver STAs that set the “Multi-STA Aggregation In Broadcast RUSupport subfield” to 1 in the HE MAC Capabilities Information field.

An HE AP may still consider separately transmitting an A-MPDU with onlyMPDU frames addressed to the STA, in a DL MU PPDU or in a DL SU PPDU fora STA that sets the “Multi-STA Aggregation In Broadcast RU Support”subfield to 1. An HE AP still considers separately transmitting anA-MPDU with only MPDU frames addressed to the STA, in a DL MU PPDU or ina DL SU PPDU for a STA that sets the “Multi-STA Aggregation In BroadcastRU Support” subfield to 0.

If the AP doesn’t support generating an A-MPDU that contains framesaddressed to several stations, HE AP has to consider separatelytransmitting an A-MPDU with only MPDU frames addressed to a single STAin a DL MU PPDU, or with only broadcast MAC frames in a group RU. Thisapplies even if a STA has set its “Multi-STA Aggregation In Broadcast RUSupport” subfield to 1.

At step 1804, the AP transmits the built A-MPDU in a DL group(broadcast) RU.

FIG. 18 b illustrates, using a flowchart, steps performed by a non-APstation when receiving data from the AP.

Steps 1811 and 1812 concern, respectively, advertising the capabilitiesof the station to the AP and receiving the advertised capabilities ofthe AP. These steps can be executed in any order and may be performed atan early stage such as the discovering phase as discussed above.

At step 1813, the station receives an A-MPDU in a DL group (broadcast)RU and at step 1814 the station extracts MPDU(s) addressed to it fromthe A-MPDU depending on the capabilities of the AP and/or thecapabilities of the station.

In one implementation of step 1814, if both the AP and the station haveset their “Multi-STA Aggregation In Broadcast RU Support” subfield to 1,the station compares a MAC address of each aggregated data frame (the RAfield 210 of each MPDU forming the A-MPDU) with its own MAC address.This is to retrieve one or more data frames, if any, addressed to thestation, from amongst the received aggregated data frames. The STA maythus retrieve one or more frames, carried in a RU intended for multipleSTAs, that are addressed to this STA based on the RA field of each MPDUframe.

If at least one of the AP and the station have set their “Multi-STAAggregation In Broadcast RU Support” subfield to 0, the A-MPDU shouldn’tcontain MPDUs for different stations (unless broadcast MAC frames). Inthis case, the station may compare a MAC address of one, preferably thefirst, MPDU of the A-MPDU, with its own MAC address. If the MAC addressmatches its own MAC address (or if the MAC address is a broadcastaddress), the one or more MPDUs contained in the A-MPDU may all beconsidered to be addressed to the station. They are thus all extractedfor processing by the station. If the MAC address does not match its ownMAC address (and the MAC address is not a broadcast address), theextraction of MPDUs (de-aggregation) is stopped as it is assumed that nofurther MPDUs are destined for the station.

Note that in an implementation variant, the feature of allowingaggregated MPDUs in a same A-MPDU to be addressed to different stationsis considered as optional only for a non-AP station and mandatory for anAP. In other words, a non-AP station still has to indicate support forreceiving an A-MPDU that contains frames addressed to several stationsin a DL Broadcast RU, whereas the AP does not have to advertise aboutits capability regarding this feature as the AP would support thefeature by default. In this variant, the MSAS subfield is added only inthe capabilities advertised by a station. This variant is advantageousbecause it provides a good trade-off between efficiency and cost of thesystem. In fact, it is preferable that the AP implements the feature tomake it effective for all the stations of the managed cell, while astation may not implement the feature without impacting the usage of thefeature for other stations of the same cell.

FIG. 19 shows examples of RU configuration between MU Downlinktransmission 1420 and MU Uplink transmission 1440 (cf. FIG. 14 ).

The configuration example identified by 1904 shows a case in which theAP considers separately transmitting an A-MPDU with only MPDU framesaddressed to the STA7 in a DL MU PPDU, since STA7 had set the “Multi-STAAggregation In Broadcast RU Support” subfield to 0.

The configuration example identified by 1901 shows a case in which theAP considers separately transmitting an A-MPDU with only MPDU framesaddressed to the STA2 in a DL MU PPDU, although STA2 had set the“Multi-STA Aggregation In Broadcast RU Support” subfield to 1.

The configuration examples identified by 1902 and 1903 show a case inwhich the AP always make one group RU with a given AID appearing once.In the examples, the group RU with AID=2045 is sent first in a DL MUPPDU 1020 a, then the group RU with AID=2045 is sent further in asubsequent DL MU PPDU 1420 b.

The configuration example identified by 1905 shows an alternateimplementation to the above description with regards to FIGS. 18 a and18 b . In this alternate implementation, the AP aggregates MPDUs in asame A-MPDU to be addressed to different stations while one of theaddressee stations does not support the aggregation feature (the stationMSAS capability subfield is set to 0). For this implementation variant,the AP builds the A-MPDU by having the MPDU(s) for the station notsupporting the optional first in the aggregation of the A-MPDU. As aconsequence, the station that is recipient of the first MPDU(s) (anddoes not support the aggregation capability), will retrieve the firstMPDU(s) as the comparison of the MAC addresses will result into apositive match; then the station may either stop retrieving followingMPDUs as soon as an MPDU intended for a different station is found, orretrieve all following MPDUs and throw away later the MPDUs with a nonmatching address.

In the configuration example identified by 1905, the first MPDU frame(s)to appear in the multi-station A-MPDU according to an implementation ofthe invention can be destined to a station that has indicated no supportof the multi-station aggregation capability by setting the bit 1721 setto 0. This station will handle decoding of those first MPDU frame(s),and then stops once it receives the MPDUs intended to station STA8. Inthe example, the station STA8 is a station that has indicated support ofthe multi-station aggregation capability by setting the bit 1721 set to1, and is able to receive the subsequently aggregated MPDU frame(s).

When one or more MPDUs with different RA values are aggregated withother MPDUs in an A-MPDU, the following ordering rule applies: TheMPDU(s) for one non-AP station that does not support of the “Multi-STAAggregation In Broadcast RU” functionality (if any) shall be the firstMPDU(s) in the A-MPDU.

FIG. 20 illustrates, using a flowchart, an implementation exampleaccording to the invention of a process of building an A-MPDU executedby the AP (e.g. step 1803 of FIG. 18 a ) taking into account the MSAScapability subfield values advertised by stations. It is assumed in thisexample that the AP supports the feature of allowing aggregated MPDUs ina same A-MPDU to be addressed to different stations, either by defaultor after the AP has advertised to stations a MSAS capability subfieldset to 1.

At step 2001, a list of addressee stations to which the AP has MACframes to send in Downlink transmission is obtained, and then theaddressee stations are processed sequentially (loop at step 2002). Theloop may continue until all addressee stations have been processed (i.e.end of list reached), and then the one or more A-MPDUs built (embeddingthe MAC frames) are transmitted in respective one or more allocated DLRUs (step 2016). In a variant, the loop is stopped when one A-MPDU isbuilt and can be transmitted in one allocated DL RU. The process thenrepeats with an updated list of addressee stations at step 2001, andother DL RUs are used for transmission.

At step 2003, it is checked if the station (currently selected in thelist) has advertised a MSAS capability subfield set to 1.

If the checking is positive (yes to the test of step 2003), the AP(scheduler) determines at step 2004 whether to use a multi-destinationRU for the station or not. This means that the AP determines if it iswilling to group distinct addressee stations to which the AP has MACframes to send in a same multi-destination RU (and hence an A-MPDUaggregating MPDUs for distinct addressee stations). Situations in whichit may be advantageous to group distinct addressee stations may besimilar to those exemplary situations described for step 1310 of FIG. 13a . For example, if a large amount of data is pending for transmissionto a given station, it is preferable to allocate a dedicated RU for thatstation. Another example is the case where no more space is left in agroup RU, then a dedicated RU is allocated to the station. By allocatingthe dedicated RU within the same HE MU PPDU, it avoids waiting foranother HE MU PPDU and thus time is gained (particularly if it is notallowed to allocate a plurality of group RUs within a same HE MU PPDU).

If it is determined at step 2004 that a multi-destination RU is to beused for the station, then a multi-destination RU is allocated at step2005, if needed. Step 2005 is optional because the multi-destination RUmay have been already allocated. A new multi-destination RU may need tobe allocated if there is not one already allocated or if a previouslyallocated multi-destination RU has no more space left.

At step 2006, one or more MAC frames intended for the station areselected for insertion in a current A-MPDU.

Optionally, the AP has to signal using UMRS Control field which responseRU the station has to use to acknowledge its MAC frame(s). This is madethrough steps 2007 and 2008 to signal in a selected MAC frame addressedto the station a UMRS Control field identifying a response resource unitto be used by the station in the MU Uplink transmission following MUDownlink transmission to provide a response to data frames to the accesspoint. Steps 2007 and 2008 are similar to steps 1610 and 1611 of FIG. 16a , and are not executed if for example no acknowledgment is requiredfor none of the aggregated MAC frames.

The selected MAC frame(s) is(are) then aggregated at step 2009 withpossibly other MAC frame(s) for distinct addressee stations in anA-MPDU. Possibly, the aggregation can be limited to one MPDU, i.e. theA-MPDU contains a single MPDU.

If the checking is negative (no in the test of step 2003), or if it isdetermined at step 2004 that a multi-destination RU is not to be usedfor the station, then step 2010 is executed.

At step 2010, it is determined if the station is already associated withthe AP. If the station is already associated, a single-destination RU(with AID of the station) is allocated (step 2011). If the station isunassociated, a multi-destination RU (e.g. with AID=2045) is allocated(step 2012).

One or more MAC frames intended for the station are then selected (step2013) and added to the A-MPDU (step 2016).

Similarly to steps 2007 and 2008, steps 2014 and 2015 can optionally beimplemented for signaling using UMRS Control field which response RU thestation has to use to acknowledge its MAC frame(s). This is particularlyrelevant for unassociated stations (no AID assigned yet).

Note that the branch of steps 2005-2009 and the branch of steps2010-2016 may be executed in parallel. Note also that it is notnecessary to have both branches in the process, and only one of them maybe executed. For example, only branch of steps 2005-2009 can be executedif the AP uses a multi-destination RU for all stations, or only branchof steps 2010-2016 can be executed if the AP does not support thefeature of allowing aggregated MPDUs in a same A-MPDU to be addressed todifferent stations.

When one or more MPDU Frames with different RA values are aggregatedwith other frames in an A-MPDU (steps 2009 and/or 2016), the followingordering rule may apply: The MPDU frame(s) for one non-AP station thatdoes not support the “Multi-STA Aggregation In Broadcast RU”functionality (if any) is(are) the first MPDU frame(s) in the A-MPDU.

In an implementation, the matching in terms of RU profile between anuplink RU already used by a station in the MU Uplink transmission and adownlink RU the AP will use in the MU Downlink transmission to provide aframe to the same station (cf. FIGS. 10 a to 10 c ) is considered as anoptional feature.

For the feature discussed in this implementation, one capability bit isadded to reflect the support of this feature. The capability bit isreferred to as “UL/DL matching profile support”, or UMPS capability bitfor short.

The UMPS capability bit can be added in the HE MAC CapabilitiesInformation field, similarly to the MSAS capability bit, e.g. in thereserved subfield of field 1710 (cf. FIG. 17 ).

Note that it may be envisaged that only one of the features “Multi-STAAggregation In Broadcast RU Support” and “UL/DL matching profilesupport” can be implemented in a 802.11ax station. In this case only onecapability bit (e.g. bit B42) is added to signal the implemented onefeature. Alternatively, it may be authorized to have both featuresimplemented in a 802.11ax station. In this case, two capability bits areadded (e.g. bits B42 and B43).

Thus, for example saving one or more allocation scheme features thatdefine the uplink RUs in order to be used for identifying downlink RUsfor unassociated stations is performed only by 802.11ax stations thatadvertised an UMPS capability bit set to 1.

FIG. 21 illustrates, using a flowchart, an implementation exampleaccording to the invention of a process executed by the AP taking intoaccount the UMPS capability subfield values advertised by unassociatedstations during discovering phase. It is assumed in this example thatthe AP supports the UL/DL matching profile feature, either by default orafter the AP has advertised to stations a UMPS capability subfield setto 1.

In the following description a predefined identifier value of 2045 ischosen to designate MU DL RUs reserved for unassociated stations. Ofcourse this value is given for illustration only and any otherpredefined value or signalling means may be adopted.

At step 2101, the AP determines whether there is a list of pendingframes (e.g. authentication or association response management frames)waiting for transmission to unassociated stations.

If the list of pending frames is not empty, it is determined at step2102 whether the list contains one or more broadcast frames. If at leastone broadcast frame is found, it is selected at step 2103 fortransmission (more broadcast frames may be selected for transmission ina same RU). A single downlink RU with AID=2045 is included in a MU DLframe comprising the selected frame (step 2104). The downlink RU can belocated anywhere within the MU DL frame (HE MU PPDU). The MU DL framemay be built at the time of inclusion of the downlink RU with AID=2045,or may be formed earlier by module 805 of the AP, for example at thetime other downlink RUs destined for already-associated stations aredefined.

If the list does not contain a broadcast frame (test 2102 negative), thenumber of unassociated stations that are addressee of the frames pendingfor transmission is determined at step 2107. If only one unassociatedaddressee station is found, one or more frames intended for the stationare selected (step 2109) and included in the MU DL frame (step 2104). Ifthe number of unassociated stations is more than one (test 2107),further processing is performed based on the UMPS capability subfieldadvertised by the stations.

For example, if it is determined at step 2108 that all stations have anUMPS capability subfield set to 0 (do not support the feature), step2109 is executed by considering frames from only one station amongstthose stations (in current iteration of the flowchart).

If test 2108 is negative (at least one station supports the feature),one or more frames intended for stations with capability subfield set to1 are selected from the list at step 2110. Preferably, all responseframes that follow the reception of request frames received on uplinkRUs from unassociated stations are selected in order to be transmittedto the corresponding unassociated stations. The design of the downlinkRUs with AID=2045 for the response frames can be based on at least oneallocation scheme feature of the uplink RUs used by the unassociatedstations. Of course, the response frame for a specific unassociatedstation will be sent over the downlink RU matching the allocation schemefeature of the uplink RU used by the same station when requesting theAP.

The number of frames selected at step 2110 may be limited to a number ofdownlink RUs available, for instance of downlink RUs available to beassigned to AID=2045. In particular, amongst the RUs available to beassigned to AID=2045, one (e.g. first) may be reserved for anot-yet-associated station that does not support the feature, i.e. UMPScapability subfield set to 0 (cf. step 2112).

At step 2111, one or more downlink RUs with AID value 2045 are includedin the MU DL frame and comprising the corresponding selected frames. TheMU DL frame is previously built or is built at the time of theinclusion. The included downlink resource unit(s) with AID=2045 matchthe allocation scheme features stored for the corresponding unassociatedstations respectively (i.e. each downlink RU matches the allocationscheme feature of the uplink resource unit used by said station to senda frame in the MU Uplink transmission).

Optionally, at step 2112, within the same MU DL frame, one RU withAID=2045 is allocated at a predetermined position, e.g. first, tocomprise one or more frames, if any, intended to an unassociated stationwith capability subfield set to 0.

At step 2105, the MU DL frame is transmitted by the AP. Finally, at step2106, the list of pending frames is updated by removing the selectedframes that have been transmitted (and acknowledged), and the steps ofthe flowchart are repeated from step 2101.

In another implementation example according to the invention of aprocess executed by the AP (not illustrated), it is assumed that theUL/DL matching profile feature is supported by both the AP and allnon-AP stations associated with the AP (either by default or determinedfollowing the advertised capabilities of the concerned 802.11 axdevices).

In this implementation example, the flowchart of FIG. 21 may be modifiedby removing the test step 2108 and the optional step 2112, and modifyingsteps 2110 and 2111. If the number of unassociated stations is more thanone (test 2107), then a plurality of frames intended for a plurality ofunassociated addressee stations are selected from the list (modifiedstep 2110). At a modified step 2111, a plurality of downlink RUs withAID value 2045 are included in the MU DL frame and comprising thecorresponding selected frames. The MU DL frame is previously built or isbuilt at the time of the inclusion. The included downlink resource unitswith AID=2045 match the allocation scheme features stored for thecorresponding unassociated stations respectively (i.e. each downlink RUmatches the allocation scheme feature of the uplink resource unit usedby said station to send a frame in the MU Uplink transmission).

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

The description above focuses on RUs that are distributed in thefrequency domain. Variants may contemplate having RUs distributed in thetime domain, in replacement or in combination with a frequency-baseddistribution. In any case, the allocation scheme features describing aspecific RU may be obtained from the allocation scheme used.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

1. A wireless communication method in a wireless network comprising anaccess point, the method comprising the following steps at a station notassociated with the access point: receiving, from the access point,multi-user, MU, Physical layer Protocol Data Unit, PPDU, comprising afield in which a plurality of downlink resource units used for MUdownlink transmission from the access point within a transmissionopportunity granted to the access point are allocated using associationidentifiers, AIDs; determining a downlink resource unit which has beenallocated to a specific AID which is reserved for stations notassociated with the access point, from the plurality of downlinkresource units, wherein the specific AID does not identify individualone of the stations not associated with the access point and is equal to2045; and receiving a frame from the access point on the determineddownlink resource unit, wherein the received MU PPDU is an MU PPDU ofIEEE 802.11 standard series.
 2. The method of claim 1, wherein theplurality of downlink resource units includes at least one downlinkresource unit which has been allocated to an AID identifying a specificone of stations which has been associated with the access point.
 3. Themethod of claim 1, wherein at most one of the plurality of downlinkresource units can be allocated to an AID identifying a specific one ofstations which has been associated with the access point.
 4. The methodof claim 3, wherein more than one of the plurality of downlink resourceunits can be allocated to the specific AID.
 5. The method of claim 1,wherein the frame from the access point carries a probe response or anauthentication response.
 6. The method of claim 1, further comprising,at the station, checking whether the frame received on the determineddownlink resource unit is addressed to the station, prior to decodingthe frame.
 7. A wireless communication method in a wireless networkcomprising an access point, the method comprising the following steps,at the access point: generating multi-user, MU, Physical layer ProtocolData Unit, PPDU, comprising field in which a plurality of downlinkresource units used for MU downlink transmission from the access pointwithin a transmission opportunity granted to the access point areallocated using association identifiers, AIDs, wherein the plurality ofthe downlink resource units includes a downlink resource unit which hasbeen allocated to a specific AID which is reserved for stations notassociated with the access point, and wherein the specific AID does notidentify individual one of the stations not associated with the accesspoint and is equal to 2045; and sending the generated MU PPDU, whereinthe generated MU PPDU is an MU PPDU of IEEE 802.11 standard series. 8.The method of claim 7, wherein the plurality of downlink resource unitsincludes at least one downlink resource unit which has been allocated toan AID identifying a specific one of stations which has been associatedwith the access point.
 9. The method of claim 7, wherein at most one ofthe plurality of downlink resource units can be allocated to an AIDidentifying a specific one of stations which has been associated withthe access point.
 10. The method of claim 9, wherein more than one ofthe plurality of downlink resource units can be allocated to thespecific AID.
 11. The method of claim 7, wherein the frame from theaccess point carries a probe response or an authentication response. 12.A non-transitory computer-readable medium storing a program which, whenexecuted by a microprocessor or computer system in a device, causes thedevice to perform the method of claim
 1. 13. A non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device, causes the device toperform the method of claim
 7. 14. A wireless communication deviceforming a station not associated with an access point in a wirelessnetwork, the device comprising at least one microprocessor configuredfor carrying out the steps of: receiving, from the access point,multi-user, MU, Physical layer Protocol Data Unit, PPDU, comprisingfield in which a plurality of downlink resource units used for MUdownlink transmission from the access point within a transmissionopportunity granted to the access point are allocated using associationidentifiers, AIDs; determining a downlink resource unit which has beenallocated to a specific AID which is reserved for stations notassociated with the access point, from the plurality of downlinkresource units, wherein the specific AID does not identify individualone of the stations not associated with the access point and is equal to2045; and receiving a frame from the access point on the determineddownlink resource unit, wherein the received MU PPDU is an MU PPDU ofIEEE 802.11 standard series.
 15. The wireless communication device ofclaim 14, wherein the plurality of downlink resource units includes atleast one downlink resource unit which has been allocated to an AIDidentifying a specific one of stations which has been associated withthe access point.
 16. The wireless communication device of claim 14,wherein at most one of the plurality of downlink resource units can beallocated to an AID identifying a specific one of stations which hasbeen associated with the access point.
 17. The wireless communicationdevice of claim 16, wherein more than one of the plurality of downlinkresource units can be allocated to the specific AID.
 18. The wirelesscommunication device of claim 14, wherein the frame from the accesspoint carries a probe response or an authentication response.
 19. Thewireless communication device of claim 14, wherein the microprocessor isfurther configured to check whether the frame received on the determineddownlink resource unit is addressed to the station, prior to decodingthe frame.
 20. A wireless communication device forming an access pointin a wireless network, the device comprising at least one microprocessorconfigured for carrying out the steps of: generating multi-user, MU,Physical layer Protocol Data Unit, PPDU, comprising field in which aplurality of downlink resource units used for MU downlink transmissionfrom the access point within a transmission opportunity granted to theaccess point are allocated using association identifiers, AIDs, whereinthe plurality of the downlink resource units includes a downlinkresource unit which has been allocated to a specific AID which isreserved for stations not associated with the access point, and whereinthe specific AID does not identify individual one of the stations notassociated with the access point and is equal to 2045; and sending thegenerated MU PPDU.
 21. The method of claim 20, wherein the plurality ofdownlink resource units includes at least one downlink resource unitwhich has been allocated to an AID identifying a specific one ofstations which has been associated with the access point.
 22. The methodof claim 20, wherein at most one of the plurality of downlink resourceunits can be allocated to an AID identifying a specific one of stationswhich has been associated with the access point.
 23. The method of claim22, wherein more than one of the plurality of downlink resource unitscan be allocated to the specific AID.
 24. The method of claim 20,wherein the frame from the access point carries a probe response or anauthentication response.